MadMapper 5.6.6 being used - OSC controls being configured for <Media>/position/ /position_sec/ and /position_frame/ all seem to have the same issue if you try to send an OSC command with an integer of zero. After starting a video loop (at least mp4, I haven't tested other video formats) with or without video hardware acceleration it will not take a "/position_sec/ i 0" command until approximately 280-300 seconds have passed in the video, then suddenly the command will work again to send it back to the beginning.
If you send any other number, it works every time no matter how far the video has played.
This was very frustrating to run into, and then try to find out why one of our exhibits was taking 2 different /position_sec/ commands 100% reliably (in this case language selection to jump to the correct language), but 2 other systems were not reliable when I was trying to force sync between them.
So I have a workaround now, posting this to hopefully at least help someone else who might run into the same bug, and maybe so it can be fixed - not sure if this would be fixed in 5.x - I don't have 6.0 beta installed yet to see if it's still an issue with it.