From what I understood, it's related to SFML, not to sfeMovie. Thus I guess I can't do much about it, or did I miss something?
Yes, the problem is either something in SFML or in the radeon driver. I will try using the catalyst driver to see if the same thing happens, but my guess is that it only affects the open source driver.
EDIT: The catalyst driver does not have this issue.
I've compiled the ffplay that comes with the ffmpeg in the deps directory to see if the problem is swscale, but it plays (almost) without problems with it.
note: I compiled ffmpeg with the flags used by the build script + the --disable-avfilter flag since ffplay uses it instead of swscale if compiled.