As has been theorized, this was indeed a side effect of this fix. We have a lot of these popups, and it turns out they're all slightly different.
I've fixed these so far:
- LQP deletion comment (the one you reported; also here)
- moderator flag decline reason
- suggested edit rejection
I've also found these, they're not yet fixed but I'm working on it:
- bounty reason
- moderator message template
- community team message template
I think that's all, but please report any others you find.