The other thing to watch out for is taking off from a high airfield underneath airspace with QFE set. Crosland Moor at Huddersfield is a good one for that, there's class A at 3,500 and class D at 3,000. Field is at 800 odd feet, easy to forget on the climb out, seen it happen.
The answer to this problem is to discontinue use of QFE, as previously discussed in
this thread.