Matroska's native MPEG-4 mode

[Doom9]

To no longer abuse the encraw thread (http://forum.doom9.org/showthread.php?t=98469&page=4) with OT comments, I'm opening this thread.
Where would using the native MPEG-4 mode break compatibility when MPEG-4 ASP is concerned? And where would it work without problems?

[bond]

i guess it breaks things with all mkv tools not supporting it (obviously), thats virtualdubmod and gabests, now old, mkv splitter