Issue explained, see below.

Bug overview description. Attempting to only include certain file types (plural) in your search, for example "anthro ~type:png ~type:jpg ~type:gif" will only return posts that literally have "type:png" etc. as one of their tags.
What part(s) of the site page(s) are affected? Search
What is the expected behavior? That only png, jpg, and gif files are included in the search.
What actual behavior is given instead? A post is returned that includes a "type:gif" tag (despite the fact that it is an animated PNG)
Time of incident (if applicable). N/A
Can you reproduce the bug every time? Yes
What steps did you take to replicate this bug? Attempt to use ~ syntax with file types as described.
Errors or other messages returned (if any). No error messages are displayed.