You don't take screenshots of cutscenes, do you? If you do, that is the problem. The cutscenes have in OFP -as long as you don't change it, because I think it can be changed when making the script for the scene- cinema borders. You can't do too much about it.
If you do not take screenshots of cutscenes, then I don't know why it happens. Perhaps something related with your graphic card or something like that.