@matmarex Is it expected that these transformations apply to regular article content? I found this surprising, but perhaps I misunderstood the intent, or maybe there's something wrong with this page causing it to be run.

E.g. at https://www.mediawiki.org/wiki/ResourceLoader/Architecture#Flipping

<h3>
  <span class="mw-headline" id="Flipping" data-mw-comment="{&quot;type&quot;:&quot;heading&quot;,&quot;level&quot;:0,&quot;id&quot;:&quot;h-Flipping-Resource:_Styles&quot;,&quot;replies&quot;:[],&quot;headingLevel&quot;:3,&quot;placeholderHeading&quot;:false}">
    <span data-mw-comment-start="" id="h-Flipping-Resource:_Styles"></span>
    Flipping
    <span data-mw-comment-end="h-Flipping-Resource:_Styles"></span>
  </span>
  <span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ResourceLoader/Architecture&amp;action=edit&amp;section=13" title="Edit section: Flipping">edit</a><span class="mw-editsection-bracket">]</span></span>
</h3>

In T291833#7386113, @Krinkle wrote:

@matmarex Is it expected that these transformations apply to regular article content?

On mediawiki.org, I think it is—DiscussionTools uses $wgExtraSignatureNamespaces to determine in which even-numbered namespaces to run, and mediawiki.org (along with other “special” wikis) has this variable set to [ NS_PROJECT, NS_HELP, NS_MAIN ] since 6c6cbb0b9082. This setting may need to be reconsidered, though, there are quite some wikis in rOMWC dblists/special.dblist that don’t have wikitext discussions in the main namespace (Commons has galleries, Wikidata has items, Wikispecies has taxa, multilingual Wikisource has works etc.).

Yes, what @Tacsipacsi said. I'll add that I filed T291630 about the weird configuration (I originally filed it about Commons, but I guess it applies to other wikis as well). Also, the extra markup should have no effect, if the page doesn't actually contain any comments with signatures.

Thanks for that link, by the way… I didn't even remember that this is partially my fault ;)

All issues should be resolved, only waiting for train deployments and QA.