Hold on. I got a 7D file (mov) from some other site. (if you still want to UL something, go ahead, the more the better).
I get thumbnails in Explorer with no problems, either with the original .mov file or repacked as .mp4 or .mkv
My DirectShow filter chain in Windows (which is mirrored in MC's settings for the above file formats) is
Haali (Source/Splitter) -> MPC Video Decoder -> EVR
-> Default DirectSound (there is no audio decoder, the sound is PCM)
Now, I AM getting thumbnails in MC (all - mov, mp4, mkv). The files get parsed OK, I got the duration and bitrate using either DirectShow or QuickTime engine for the MOV file and DirectShow for the other 2 containers. Thumbs show up. And both analyzing and thumbnail grabbing show up OK in MC's log. QuickTime engine is no good when it comes to playing, is stuttering like hell, stay with DirectShow.
So I guess it's a matter of having the right (and most recent) filters. MC 14.0.121, Win7 x64.