The whole piece is very much worth reading, but I can't decide if I think this argument about punctuation is brilliant or over-ingenious:
Walpole’s love of display was as great as his love of mystery, and the public could apply for tickets to view Strawberry. What they were allowed to see, a daring mixture of styles and an apparent flouting of the principles of taste, was shocking enough to some. In the Preface to the Description, Walpole prepares the reader for Strawberry’s “heterogeneous” combination of “obsolete architecture . . . French porcelaine, and Greek and Roman Sculptures”, describing it as a mixture that “may be denominated, in some words of Pope, ‘A Gothic Vatican of Greece and Rome’”. Here once again, however, Walpole was playing tricks with the poet’s memory. Pope’s line, from the Dunciad, refers to the meretricious library of Bayes, the laureate of dullness. This collection of worthless volumes is not at all mixed; it is, as the lines read in the original: “A Gothic Vatican! of Greece and Rome / Well purg’d”. Walpole’s interference with the text is telling, for, whether it was Pope or Popery, literature or architecture, what he was concerned with was realizing his own ideas. The removal of Pope’s punctuation had a parallel in the collaging of medieval motifs in his house where Walpole used prints of Gothic tombs as models for his chimneypieces. The choir screen from old St Paul’s Cathedral gave his friend John Chute an idea for fitting out the library, and the exhibition includes Walpole’s copy of William Dugdale’s History of St Paul’s of 1658 with the relevant detail carefully snipped out.But what if it's not so much Walpole playing tricks with Pope's memory as Walpole's memory playing tricks on him? Pope's couplets do occasionally use enjambment to string a thought across a line break, as in the line quoted, but it is a sort of reversion to the mean when Walpole keeps the ringing and conclusive line-segregated phrase and omits the rest: in other words, it seems to me as likely to be an almost philistine opportunism (or a serendipitous misremembering, as the verb collaging suggests) than something over which Walpole himself would be likely to have had conscious awareness or control.
A wide prevalence of misquotings is a natural byproduct of a culture in which readers are as likely to have access to versions of poems held in their memories as to the books in which they encounter them; here were some of John Haffenden's thoughts a few years ago on William Empson as a notorious misquoter, in the best tradition of Hazlitt and others.
I realize that I have not dipped into Walpole's correspondence since graduate school - time for another look, perhaps...
Bonus eighteenth-century link: at the Nation, Sam Moyn's devastating take-down of Jonathan Israel's A Revolution of the Mind: Radical Enlightenment and the Intellectual Origins of Modern Democracy.