I use Drag method on a Java Slider with some number as argument. It fails to work during execution. But always works with breakpoint. Any setting to make QTP simulate execution behavior of breakpoint. Please note that application is thick client Java.
I've come across this problem in the past and I found it was because QTP/UFT was getting ahead of its self. This might seem primitive but I had a sync (to ensure that your application has displayed the expected page), put a couple of second wait, check that 'Slider' exists and then attempt an action on it.