"Import project files" gives you four slots to import, via a URL like:
http://thewiki/index.php?title=Special:ImportProjectFiles&project=theproject
If you don't use all four slots, then after hitting upload, the remaining slots are still present, on a page with a URL like:
http://thewiki/index.php?title=Special:ImportProjectFiles&action=submit
and is still titled at the top e.g.
"Import Project Files:
Use this form to upload files to project theproject. "
Using this form will import files, but not to the desired project, which can lead to consternation and confusion.
Anonymous
I think https://sourceforge.net/p/workingwiki/bugs/258/ is going to be the answer to this (rewrite the import page). The new one will have to make sure not to inherit this problem, so I'll link that back to here.