DirectShowSource load MKV with Subtitle reports no video

[huang_ch]

I've reported this to sourceforge bug section:

Summary:
load mkv files incorrectly
When using DirectShowSource to load a external .MKV
file which contains subtitles, no video is loaded.

Reproduce:
Method 1:
a) Write a .AVS to load a external .MKV file
b) Use MPC or other media player open it
c) Only audio will be played
Method 2:
a) Write a .AVS to load a external .MKV file
b) Use VD/VDM open that AVS
c) It reports "no video"

And, when I use tools to re-mux that MKV file with no
subtitle, all works fine.
Also, I use GraphEdit open that MKV, it also works fine.