VVVVVV--
So, uh...
Masto's webui has that "filter by regex" option. And it takes regexen, as it should.
A single letter -- v, specifically -- is a valid regex. I wonder how long that'd been there. Got a lot more toots to read now.
UX suggestion: have a visible "(Filtered)" in the header of any column with an active filter so people can at least know a filter is active.