This should fix an issue where events with negative duration (frame end before frame start) are not correctly addressed.
Done by adding only events to the clipboard that have the event position
DURING and by resetting the event if the marker
UNKNOWN is found.
Background: Without this fix, an event with negative duration leads to the event being added to the current event. For the consecutive runs, the bad event keeps being read and the run loop is stuck on this particular event.