MPEG-4 Media Foundation Source stubbornly keeps marking a second video sample with a MFSampleExtension_CleanPoint flag even though nothing suggests that the video frame is an IDR frame.
The actual video frame is a P frame both in terms of MP4 box formatting and contained NAL units (the video is in fact an “infinite GOP” flavor of recording where all frames are P frames except the very first IDR one).
The problem is specific to fragmented MP4 files (and maybe even a subset of those), however is pretty much consistent and shows up with both H.264 and H.265/HEVC video.