When Special:Contributions is transcluded onto a page, it causes all <math> tags on the page to produce strip markers instead:
The math is rendered properly in the preview window though. This can be seen in action in my sandbox (and on my userpage). It only started happening within the last few days, I think.
In addition to this, the list elements in the transcluded output are now broken over multiple lines, sort of like how the watchlist was misbehaving a few weeks ago.
This behavior is reproducible in Firefox and Chrome, while logged in and anonymous.