MKV and buffering...

I've never liked MKV for one simple reason. Whenever I try to seek in an HD file, it always pauses for about a minute while filling up a buffer. With TS and M2TS containers I never have this problem. Is there any solution for this?

Did you try a different splitter? (using Haali's Media Splitter seeking in HD files works fine here,..)

I use Haali. The files I have trouble with are those created by MeGUI, which I think just uses the default X264 muxer to create the MKV container. If it's not something common I can just see it with the MeGUI / X264 team.

Before or after you mux them? You'll always get the "buffering" for MKV files directly created by x264 because they have to be written differently than normal MKV files since some of the required information is only available after the encoding finished. After you mux them with audio or simply mux the video only to MKV again that issue will be gone. MeGUI uses mkvmerge to create MKV files.