Quatermain

Hello, i do have some problems with small corners 400mm by 400mm, When I have them right, and i want to change something else on the other side of the wall, the corner will be automatic delete. Even locking walls does not make a differents. changing wall connecties does also not fix the problem. try with different layout of walls, i notices only that the problem is more when the thickness of the wall is bigger. The problem is in any versions of chief architect. Is there anyway to fix this?