easy to reproduce:
download mission, or go to editor
1. place a trigger:
Bluefor / Repeatly / Present
ON ACT. {}
ON DEA. {hint "OMG";}
2. place the player, a blue rifleman, into trigger area
3. place some green soldiers into the triggerarea
4. set "Independents are friendly to: Bluefor" (weathersettings)
5. click PREVIEW
6. don't move and shoot down some greens
If the player don't move the bluefor trigger deactivation {hint "OMG";} should never run, but
result is: the Bluefor-Trigger fires up the deactivation-event, the hint "OMG" will be shown on screen. And no error will be displayed.
If there are more triggers on the map then they are all deactivated after this error happen.