I'm puzzled. The reason is that I've just read Merja Kytö, "Be/have + past participle: The choice of the auxiliary with intrasitives from Late Middle to Modern English", pp. 17-86 in Matti Rissanen et al., Eds., English in Transition: Corpus-based Studies in Linguistic Variation and and Genre Styles, 1997.
The content of Kytö's chapter doesn't puzzle me — it explains very clearly how English changed from be to have as the marker of perfect aspect in intransitive verbs. This change is easy to see in bible translations, where for example in 1 Samuel 26:20, the King James Version of 1611 gives "the king of Israel is come out to seek a flea", where the 1978 New International Version of 1978 gives "[t]he king of Israel has come out to look for a flea".
And the timeline is also pretty clear. Based on tracking the use of be/have + past participle in a corpus of about 2.7 million words spanning the period from 1350 to 1990, Kytö demonstrates that "in the late Middle English period, the use of have increases gradually, gains in momentum in the late 1700s and supersedes the use of be in the early 1800s".
What puzzles me is why this process seems to have escaped the censure of prescriptive grammarians. Here's a change that "[gained] in momentum in the late 1700s", just when the likes of Robert Lowth and Lindley Murray were in bloom. Did anyone stand up against the rising tide of have for marking the perfect in intransitives? If so, their delaying action was ineffective and quickly forgotten.
I don't know much about the history of prescriptivist ideology, but I think that I may be projecting the ideology of modern preservationist prescriptivism inappropriately into the past. In modern times, it's common for would-be linguistic authorities to pretend that they're holding the line against degenerative change, even when they get the history backwards. But John Dryden initiated the condemnation of sentence-final prepositions on the grounds "that the language, wit, and conversation of our age, are improved and refined above the last". Perhaps this style of progressive prescriptivism influenced some later grammarians to see the be/have change as a step forward into a better future, rather than a symptom of how far kids these days have fallen.
Anyhow, the be/have history is an interesting one. Here's how Kytö's chapter starts:
In many languages the choice of the auxiliaries be and have (and their equivalents) has been subject to variation in perfective constructions with intransitives indicating "transition" or "change" (cf. they are arrived versus they have arrived). In some Germanic and Romance languages the development has resulted in the generalization of one construction (e.g. the almost total dominance of "be" in Present-day Danish and "have" in Spanish and Portuguese); in others both variant forms occur in certain grammatically, stylistically or regionally restricted contexts (as, e.g., in Present-day Swedish, German, French and Italian).This cross-linguistic variation reflects the differences in the systemic realizations of the distinction between state (favouring be) and action/process (favouring have). Over the successive stages of development, various linguistic and extra-linguistic factors have influenced the choice of one form or the other.
In the Old English period the be/have + past participle construction denoted "state" in instransitive and transitive uses (cf. hie wæron gecumene; hie hæfdon hine gebundenne). The past participle originally functioned as an adjective and was sometimes inflected (Mitchell 1985:1, §709). However, the grammatical concord was gradually lost and the past participle was placed immediately after the auxiliary. Have originally occurred with transitive verbs only, but early on came to be used with intranstives, too. In Early Middle English be prevailed with mutative verbs, but have started gaining ground slowing in uses with the emphasis on "action" and the notion of perfectivity (Rydén-Brorström 1987: 17-18). Signs of the rise of have are apparent from around the 1400s on (for a recent corpus-based study, see Elsness 1989: 100; 1991: 276-283).
Kytö summarizes some ideas of David Denison's about what happened when, and why:
The development of be and have perfects show features attributed to the process of grammaticalization, but scholars disagree about the exact chronology and nature of the process. A recent discussion on the topic can be found in [David] Denison [English historical syntax: Verbal constructions] 1993: 340-368 … With have perfect the relevant factors have been the loss of inflections in the participle, the word order, and certain VP types (according to the semantics of OE habban and the valency of the main verb). The process of grammaticalization would have reached a stage of fulfilment "when the have perfect became available for any lexical verb which did not conjugate with be", i.e. when it became an auxiliary verb, the suggested (but debatable) date for this being the late Old English period (Denison 1993: 352). The other possible stages of grammaticalization include the point when the construction became a tense equivalent (probably in late Old English); when it had developed its present-day meaning and superseded be (probably in the seventeenth century); when it became used with all non-auxiliary verbs (in late Modern English) (Denison 1993: 352). There is, similarly, disagreement over the grammaticalization process of the be perfect (for a summary, see Denison 1993: 360-361); the factors regarded as having influenced the process include, e.g., the increasing use of be as the auxiliary of the passive and the relatively light functional load of have, the possibility of neutralizating the present tense third-person singular forms into the clitic 's, and the prescriptions of normative grammarians.
Over the two centuries since the change became essentially complete, several sources of variation — especially archaism and ambiguity with quasi-adjectival constructions — continue to generate examples that might be taken to mark the perfect with forms of be. Thus Wilfred Campbell in 1905 wrote a sentence with two apparent be-perfects ("is vanished" and "is gone"), one have-perfect ("has passed), and one be + past-participle-adjective ("is done") in parallel:
17 Where the woe that wrecked me is vanished,
18 And the pride that stayed me is gone:
19 And only the feeling of eventime,
20 When the toil of the world is done:—
21 O, Master of being and slumber,
22 When the pageant and pæan have passed;
23 Take me where thy great silence
24 Is vaster than all that is vast.
And a search of Google News turns up these current examples:
Return to the oven for 45-50 minutes, until the centre is risen and set.
We have to depend on well water that is become so orange because of all of the growth that I can no longer wash clothes at home.
He added, "Globalization is come to be known as an international avenue for profiteers to exploit workers wherever they can."
"As far as I am concerned, she is dead. I have told my children their Nana is gone to heaven," Fiona Porter said.
Most of the water is gone to the Mississippi (River) through the Embarras River, but Lawrenceville is quite similar to Montpelier with the river.
But that option is gone to New Orleans now.
An enraged and despairing Sita jumps into Ravana’s funeral pyre and dies at the end of the play, even as Rama moans “My punishment is come upon me now. My dreaded punishment is come “.
Now that they've been hit hard by losses on their huge mortgage exposures, that backing is become more explicit.
Rama's moan is probably meant to be quasi-biblical language, while "until the centre is risen and set" could be interpreted along the same lines as "until the centre is high and firm".
But whatever the source, examples continue to occur that could be interpreted as be-perfects, and it's an interesting issue in linguistic dynamics that these don't apparently generate any tendency towards a reversal of the historical process.