[bmonster]

I've tried with a few movies including ones I know were OK and its the same with every one.
Not sure a log will help with anything, but will post if wanted.

Any particular type of subtitle - internal (muxed in mkv) or external? ASS, SRT or other?

All SRT, external.

Forgot I was using estuary mod, which appears to be the problem.
They seem to be working fine with standard skin.
Sorry for wasting your time.