RC4.3 and Win8 - someone got it work?

I have serious problems getting Radar Contact to work properly under Win8 (in Win7 I had no probs at all).

Symptoms: When RC issues a command to me, FSX freezes for about 30 seconds (not every time, but most of the times).

There is one way to get rid of that - but it's of course no solution: When you click and hold your left mouse button on the RC window while FSX is frozen, the freeze is immediately gone, but only as long as you release the mouse button.

Anyone else experienced that and is there a solution to this problem?

Best,

Bernhard