on enwiki technical village pump: http://snag.gy/YhWgA.jpg

The same issue occurs in a template in fr.wiktionary with HHVM enabled: https://fr.wiktionary.org/w/index.php?title=Mod%C3%A8le:de-nom-f-n&diff=prev&oldid=18645452

Although I can't find an incorrect tag, because the template in question is a bit complicated.

Issue was also brought up on de.wp: https://de.wikipedia.org/w/index.php?title=Wikipedia:Fragen_zur_Wikipedia&oldid=135111112#Software.C3.A4nderung.3F

(In reply to darkdadaah from comment #2)

The same issue occurs in a template in fr.wiktionary with HHVM enabled:
https://fr.wiktionary.org/w/index.php?title=Mod%C3%A8le:de-nom-f-
n&diff=prev&oldid=18645452

Although I can't find an incorrect tag, because the template in question is
a bit complicated.

This is caused by Modèle:de-nom-f-n/Documentation: It contains multiple "selfclosing" <div /> tags, but these are invalid in HTML. If you want the documentation to display correctly even when HTML tidy doesn't work, you have to replace them by <div></div> (I won't be able to give an appropriate French summary for such an edit, so I can't fix it).

This also appears to be the cause of bug 72343.

Also, as I noted there, not all servers seem to be affected, and I see a "Tidy was unable to run" HTML comment in the output.

Assuming that $wgTidyInternal is false (by default, this is the case if extension_loaded( 'tidy' ) returns false), it looks like this can only happen if proc_open() or proc_close() fails when called from MWTidy::execExternalTidy().

Michael M.: thanks, the page has been corrected.

I keep here a link to the previous buggy version of the page for future tests (if needed): https://fr.wiktionary.org/w/index.php?title=Mod%C3%A8le:de-nom-f-n/Documentation&oldid=18183655

Also, the html source of the erroneous page contains the message: "Tidy was unable to run". Not that there is any doubt about it now...

• Bug 72357 has been marked as a duplicate of this bug. ***

• Bug 72343 has been marked as a duplicate of this bug. ***

Copying my analysis from bug 72357:

This appears to be bug 72205 (or more correctly, the memory leak in HHVM that bug 72205 exacerbates[1]) filling up memory on the HHVM servers, which is eventually causing the attempt to fork Tidy to fail, which is allowing unbalanced tags in certain pages to corrupt the layout.

[1]: https://phabricator.wikimedia.org/T757

In T74345#768025, @Anomie wrote:

This appears to be bug 72205

T74205 is fixed nowadays. Should this task also be closed? (No news for half a year here.) Might also close T74358 which might have same cause?