Thanks for your reply. Based on the xy-vsfilter website's FAQ I'm fairly positive it's being used properly. I have the latest stable 32-bit release (3.0.0.211).
Some details I forgot to mention:
- the video temporarily stutters or freezes but the audio keeps playing normally
- in some cases it makes MPC-HC crash
- disabling the subs during the scene prevents the problem
Here's a screenshot of a scene that caused the video to stutter and MPC-HC to crash. It's not really a text but this is the type of subtitle rendering that sometimes (though not always) causes issues:
http://img209.imageshack.us/img209/3856/tu0l.jpg