Throttle help, please

I just purchased the x-treme King Air B200 aircraft by Flight 1 software.

I am asking this question here, before i try to e-mail Flight 1 for the answer. Thinking maybe someone else had this problem on their AC.
I have the Saitek X53 flight control system. I have checked to see if it needs to be calibrated, but everything looks find.

With my throttle down to zero, i release my parking brake, and my AC starts to roll. While it's rolling, it picks up speed on the way. Making me to brake all the time. When i completely stop, i must keep the parking brake set, for it not to move. It's the only AC i have, that does this. This isn't normal for this AC, is it?

Thanks,
stocz2