@Rifane I can duplicate this IF I have "Quantize to Frames" turned OFF and it does not start on a frame boundary. Make sure "Options - Quantize to Frames - Enable Quantize to Frames" is turned on and then adjust the event so that it starts on a frame boundary.
@Rifane, when working with video media, you should ALWAYS have Quantize to Frames on. That will force all events to start on a frame boundary. If you look at the other option - Show Unquantized Event Edges - all edges that are not on a frame boundary will turn red so you can then adjust them so that they are.