Single step trap and sysenter on windows 7

Working on my own little user mode debugger, mainly for learning purposes. I am running into a problem here; I understand that a blocked sy开发者_开发问答scall means that the calling thread must wait for the routine to finish. I seem to have an issue with having the trap flag set while hitting one of these.

First question, would this normally cause a crash?

Second, what is a good method to 'step-over' these. That is, if they are actually the culprit here.

Thanks!