Mouse problem

I am using grx with DJGPP. I am having a problem in one function. By remming ot sections of code I have isolated the problem down to GrMouseGetEventT( GR_M_EVENT, &rat, 0 ); In Windows 95 I get fairly predictable results but in DOS I lock up, hard enough that ctrl+alt+del does not work, I have to use the reset button. In DOS if I single step through the function (and function calls with in my function) my function works as expected, I guess the debugger is getting in the way. If I erase the mouse pointer with GrMouseEraseCursor(); then, other than having no mouse displayed, my function works as expected from both DOS and Windows. Any ideas? (What did I do/not do?) Cheers Richard