As a purchaser of Pro-version, you're entitled to get direct email support from BS.Player team.
You can contact them
using this webform. Did you do that already?
Did you already try what happens if you use legacy (='old') subs-engine?
Type of subs? Do you have this problem with any type of video-file?
Which codecs/filters does BS.Player use for playback?
(To find out: (with a file loaded) rightclick > Options > Filters > Advanced.
(Clicking on "Source" and on the +signs in front of the filters/codecs shown, will reveal further info and access.)) 
(Did you already happen to come across
this thread?)