Question regarding Unit Enters area trigger.

[MR_BURNS2]

In an Air Defence scenario i want the trigger to fire once each time a Redfor aircraft enters one of the areas.
Problem is, once a Redfor AC enters an area the trigger fires continuously.
If i uncheck Event repeatable it fires only for the first aircraft entering.

Is it intended that way or is it a bug?

I guess i can work around it though by creating one event for every single Redfor aircraft.