The positive rate of climb isn't due to the vertical lift component of the wings. It's due to the fact that the nose is now above the horizon. Therefore, the thrust of the engine is pushing the aircraft slightly upward.
And remember, in some aircraft (not the C-101), you can do a knife edge pass using just the rudder. In that case, the wings are providing zero lift.
As an aside, I just tried the F-5E and this phenomenon is actually quite pronounced in it.