I think it was happening in older versions of Spring, too, that some low flying planes, esp. airtransports, when trying to reach big mountain or flight level of above big mountain can sometimes fly through the hill. But now it happends me really a lot.
1) Is it bug (
OR feauture

) of engine that is known?
2) And is common to solve this on side of game/mod developer
OR some actions in engine "change" are planned?
Thx.
P.S.: i think its obvious, so i dont add any image or reproduce steps