[mythtv] thumbnail preview doesn't change with bookmark

[Paul]

In the recorded program list , I have noticed that occasionally the
picture thumbnail which normally shows start + offset if at the start of
movie (if not watched) or at the current bookmark doesnt move from
original,
ie  I start watching and have the "automaticatic" bookmark when exit the
thumbnail is of last position(bookmark) . which is a good feature.
On frequent occasions it doesn't move from initally set thumbnail.
is this a bug or a random feature that I have missed?
I see no error msgs in frontend/backend log , do you need any debugging
info to reproduce?

Thanks