Double checked with parsoid, looks to be happening there

Using the following template(simplified from abuse filter page) against mediawikiwiki:

{{extension |description=<section begin=shortdesc />foo<section end=shortdesc /> }}

Parsoid escapes the section tag, the wikitext parser appears to strip it. Nick islooking into what exactly is supposed to happen and why.

Adding gwicke as this is a difference between php parser and parsoid output

The "shortdesc" text is used on mediawiki.org to populate the description column in the various Extension Matrix subpages, eg. https://www.mediawiki.org/wiki/Extension_Matrix/media

Also, it's used by WikiApiary eg. https://wikiapiary.com/wiki/Extension:Abuse_Filter

Possibly elsewhere?

I think it's defined/controlled by XGlossary, which says it's mandatory, https://www.mediawiki.org/wiki/Extension:XGlossary/Doc#The_Glossary_Entries

HTH. That's all I can find from digging around.

Seems like this has been fixed already: https://www.mediawiki.org/w/index.php?title=Topic:Rpiww40w1on9wf9p&workflow=rpiww40w1on9wf9p