Windows 7 - Overlay mixer - dark pink lane

[trodas]

I wonder, if anyone encounter this problem:

On Windows 7 some very old BSplayer fail to play many MKV/MP4 files, untill I changed the display output from "Internal renderer overlay (default)" to "Overlay mixer."

Now almost everything play well, except this problem:
- The Matrix series MKV files (all there) show like a 10 pixels high dark pink space /lane at bottom of the overlay window, visible on fullscreen too.

(looks like as the video is not cropped, but instead resized horizontaly a bit)

This happen only for these files, all other hi-res MKV / MP4 files do play w/o this dark pink stuff. I absolutely did not understand WTF is going on. Anybody ever heard about it?!