phent_getvelocity affects my entity?

Hi all =)

I set the velocity of a physics sphere. If I add a call to phent_getvelocity my entity stops moving. When I remove the line, it moves as it should. The documentation does not specify any side effects from getvelocity. It might be important to note that this is my second call to getvelocity in a single frame, so perhaps more than one is not allowed?

It seems to me that a function used to observe a system should not affect the system if possible.

How can I determine the velocity of my entity without breaking the system?

Thanks so much for your time!