Is this ANY video clip, or one particular one?  Is this time point the beginning of a clip?

If the answer to my second question is yes you may need to change a program setting (File>Settings>Program, shortcut Y), Playback tab, Arranger, Space Bar Behaviour.  You may need to put a tick in the box "Space Bar stops at current playback position".

If that is the answer please let us know!

If that is NOT the answer please post back and give us more details about your system, exactly which version of VPX you're running, the format of the video file you're having the problem with, exactly what you are doing to repeat the problem, etc.  That way we fellow-users may be able to also produce this behaviour and so suggest a work around/solution.

Jeff