You could try saving the original PPT as a PPS instead (PowerPoint Show, one of the options on the Save As menu) and upload that. A PPS is inherently read-only so you ought not to get any options to save it after closing it down again.
I hope this works for you. I'm guessing that there is some content in the original PPT which makes PowerPoint think that a change has been made but without looking at the original I wouldn't know what it was.