Help! Adding subtitles makes video stutter and sound fall behind

This is happening with several movies, and makes my vero unusable for what was intended.
I am now running raspberry model b with raspbmc to watch movies.
Am I doing something the vero was not made to handle?
Is there anything I can do to help fix this deal breaker?

Vero updated April 17th.
win 7 server with smb.
passthrough on all.
no peripherals.