C172 only, or all planes?

The sim isn't paused.   I can now release the brakes if I disable the joystick.  Wierd.   Button one (the fire button) on my Force Feedback 2 joystick doesn't release the brakes even though it's mapped correctly...and I can verify that the button works.

This doesn't apply to the 172 but in other aircraft make sure you don't have the props feathered. I've done that and wondered why the brakes were still on.

Sounds like your joystick and keyboard are fighting for the operation. Try remapping that back to the default [.] key or maybe try mapping a different button.

I don't know how your joystick is set up but I have a Logitech Wingman Strike Force with force feedback and when I mapped my trigger to the brakes I had to make sure I only mapped it to [.] "pressed" not "presse and release" to do this I recorded pressing the key then stopped recording while I was still holding down the key. I had the opposite problem  though. My brakes would come on the first time I pressed the key but then turn right off I kept having to press the trigger rapid fire to get the plane to stop. You might also look at your repeat settings. If they are set to none or low speed then you might not be getting the button activated.