Bug overview description.
Post searches such as sonic -male -female -intersex -ambiguous -zero_pictured this one (which, as of posting has zero results) will very rarely return a random smattering of around 50 posts that contain some but not all of the searched tags.

What part(s) of the site page(s) are affected?
Post searches

What is the expected behavior?
No search results

What actual behavior is given instead?
40~50 results

Time of incident (if applicable).
I believe the problem started about a week ago, I've experienced this a few of times since.

Can you reproduce the bug every time?
No, it seems to happen somewhat randomly.

What steps did you take to replicate this bug?
Open searches (containing a lot of -s) that should return no results fairly often.

Errors or other messages returned (if any).
N/A