I am using versoin 2.50 build 1017, but this behavior was observed in many old versions too.
Windows XP Pro
When BS Player is in full screen mode and the search results for subtitles online dialog appears, the following happens (and it is wrong):
1 - The cursor is not visible
Therefore, choosing a subtitle and downloading it or even closing the dialog has to be done "blind" by moving the mouse around and try to get a change in buttons color and then press Enter.
2 - Cannot close the dialog using the keyboard (, pressing escape does not close the dialog and because the dialog has the focus it is not possible to return to small screen mode to make the cursor visible)
Correction: I now saw this bug was reported and confirmed in
[CONFIRMED] [Online Subtitles Window] Mouse disappearing
(My initial search did not find it)
But not corrected yet