This has been happening for quite a long time. Even before the North East Airfield was remodeled.
If you drop a weapon or any item near trees, it won't let you pick the item back up even when you're right on top of it. I think though if you re-log you can pick them back up.

This has also happened to me on another occasion where trees were not around. I was in a Hangar at the North West Airfield one day and dropped my AKM and wasn't able to pick it back up however an enemy player that engaged me at the time was able to access the AKM on the ground. Another time after that was in the middle of a road.