[mythtv-users] Closed captions become "stuck"

[Jim Stichnoth]

I watch recordings with closed captions turned on.  Sometimes the
captions become "stuck", where a particular caption remains displayed
and none of the subsequent captions appear.  Or, less frequently, a
caption is erased and subsequent captions aren't drawn.  In both
cases, I can jump forward or backward and the captions will reappear.
Each point where this happens is repeatable -- if I skip back before
the point, the captions get stuck again at the same point.

These are recordings from an HDHR.  I think, but am not certain, that
it only happens for recordings that I have losslessly transcoded to
remove commercials.  (Unfortunately I don't have the original file for
comparison.)

I used ccextractor to create a .srt file from the most recent instance
I saw (last week's episode of "Fringe") and I looked at the parts
where captions in MythTV became stuck, but I saw nothing remarkable.
Running mythfrontend -v all showed nothing cc-related that I could
see.

Any ideas what might be happening, or where to look in the code?

Jim