The TwoColConflict extension is overriding EditPage for all ContentModel. So, it is overriding the custom EditPage subclasses used by some ContentModels like the "Page" and "Index" one of ProofreadPage, making them not possible to edit.
The "AlternateEdit" hook handler should be modified in order to don't do anything on contents that are not Wikitext.
Examples of affected pages when the TwoColConflict beta feature is enabled:
I do not manage to reproduce this issue with the 1.30mwf19 version of MediaWiki core and ProofreadPage. The root cause is maybe an other extension that also overrides this action for all content models or something related to the WM environment (content model lookup?).
User:einstein95 have found the root cause of this issue: it's because TwoColConflict and ProofreadPage does competitive overriding of EditPage. I have updated the task description accordingly.
i could save edits with index. fields did not load
additionally, in page space, header and footer field did not appear, but "noinclude" wikicode was shown, buttons to edit page status did not appear, but "pagestatus" wikicode did
See my comment on T175260#3597752. I suppose we need to fix this sooner rather than later :)
Change 379724 had a related patch set uploaded (by Legoktm; owner: Legoktm):
[mediawiki/core@master] EditPage: Extract some edit conflict code into EditConflictHelper
Change 379725 had a related patch set uploaded (by Legoktm; owner: Legoktm):
[mediawiki/extensions/TwoColConflict@master] Refactor to extend TextConflictHelper instead of EditPage
Reproduction scenario (this is how I encountered this bug):
Change 379724 merged by jenkins-bot:
[mediawiki/core@master] EditPage: Extract some edit conflict code into EditConflictHelper
Change 379725 merged by jenkins-bot:
[mediawiki/extensions/TwoColConflict@master] Refactor to extend TextConflictHelper instead of EditPage