Project Reality BF2: Flying south out of bounds crashes the COOP server. What's the reason?

Project Reality was a mod for BF2 but has now become a standalone game.
You play on maps, and when you go off the map (out of bounds) a message will tell you to get back ASAP. If you stay out of bounds for too long, you die.

The co-op servers (humans vs bots) have had an issue with this bug that causes an immediate server crash when someone uses a helicopter or airplane and flies out of bounds on the southern map edge.
North, east and west out-of-bounds trips don't cause this.

Would this be caused by a general config file error, or would it be map-based since it's triggered upon crossing a boundary? I've tried finding related documentation on the internet, but it's hard to get by. Articles on map boundaries in other games don't prove useful and don't explain the exact mechanic behind it.

The issue occurs on many maps, but seemingly only with aerial vehicles. Thus making me think it's the boundary code since there is a small boundary for ground and a larger one for aerial vehicles. I could, of course, also be completely wrong.