Hi Gyri,
I had a similar problem on my 30% Lanier Edge with Hitec 5945 servos driving the elevators.
the plane would sbap inverted every time I pulled into a wall or did a parachute or would spiral out in a elevator.

I tried re-programming the servos several times using pointers taped to the elevators to make sure that the travels matched exactly. Not just at the end points, but I had them moving as close to identical thru out the entire movement range.
Still, the problem in the air was not getting any better, still snapped like it was a heavy loaded Cap.

I was about to give up trying on that day but I decided to try one more thing just out of frustration.

Since my plane kept snapping to the right, I programed my end points of the left elevator to actually move more than the right elevator.
Went up into the air and, what do you know, no more snapping! Now it drops into elevators, and harriers, walls no longer flip inverted.
I know this is probably not the right way of solving the problem, but I ran out of other ideas.
Had already balanced the plane laterally too. So far it seems to be working. I'll try to get some more trim flights in to see if anything weird shows up.

Its worth a try and cost nothing and just a few quick blips on the transmitter. If it doesn't work, just blip back to your old setting.