Interesting but I don't get any errors nor do I have any empty files... The file upload USED to work and I discovered this when I upgraded to 7.4.X. I thought I read somewhere here that this was fixed for 7.5?
Anyway - I see you have registered so I'll approve your reg so you can see what's up - I made a test post in the "Site Hub & Member Involvement" category called "Test Post." Clickie on the attachment linkie and see for yourself or try to attach something in a reply.