I'll take that as "yes, the IMediaSeeking and IQualityControl functions are buggy, please don't make it worse".
Ah yes, our IMediaSeeking::SetPositions is missing the lock, I didn't realize that one was implemented directly...
IQualityControl is different because it's supposed to be done on the streaming thread, and those shouldn't take the filter lock. Threading in DirectShow gets complicated :-/