Ah sorry, that was my tag. I should have tagged it as CSS instead of css-sanitizer.

This was resolved by https://phabricator.wikimedia.org/T308160. It is now possible to use -webkit-filter (although the unprefixed filter should be preferred anyway).

Note that this issue is not exclusive to mode=packed — it affects all gallery modes. The following are examples of the different gallery modes from Help:Gallery tag, all displaying this same issue.

This behavior appears to originate from https://phabricator.wikimedia.org/diffusion/SMIN/browse/master/skinStyles/mediawiki.page.gallery.styles/tablet.less

I believe this is the same issue as T308160

I would like to echo this concern. The fact that the edits are completely hidden from logging even when viewing bot edits makes me extremely concerned about the traceability of edits made this way.