VobSub Removes MPC's Subtitles

I installed VobSub (so I could use VirtualDub to permanently embed subtitles into the video), but now videos no longer display separate external subtitles when I open them in Media Player Classic. Auto-load subtitles is checked in MPC.

I can get them to work if I use "DirectShow Video: VMR7 (renderless)" in MPC, but then the video gets too light. How do I get external subtitles to show using "DirectShow Video: System Default" in MPC?

MPC (unicode build) 6.4.9.0
VobSub 2.23
Windows XP (64-bit)