I have real problems with Reaktor4 also.

I use it with Logic6.2 and it really sucks power. I agree that Reaktor is an awesome tool but it is really unreliable.

for example: I find that if I sequence a fairly complex synth line that reaktor may only play some of the notes...and then other times play all of them...some times it plays out of tune...

This is a real problem, and has kept me from using Reaktor as much as I would like. Plus, the damn program was fairly expensive for how buggy and unfriendly it is.