Trouble getting fully valid files with matroskamux

[Pedro Côrte-Real]

I've been using matroska as a container for h264 and am having trouble
getting correct file sizes when read by totem/vlc:

1) When streamed from a live source (rtsp) vlc/totem don't know the
video length at the beginning of playback
2) When concatenated from several demuxed mkv files the total length
is correct, the total file size is correct too, but when it gets to
the end of the length of the first original file the stream stops
playing
3) vlc always complains of "mkv demux error: Cluster too big, aborting"

Any ideas what the issues are here? I've tried tweaking
min-index-interval without much difference I could find.

Pedro