Thanks for the replies guys. I think it may have to do with when I'm flying a plane that requires long slow turn fights in the weeds. I flew a different plane last night where I wasn't getting involved with having the stick yanked all the way back and holding it there as the nme and I circled each other down in the weeds and it didn't happen a single time. I'll try to take note of when it does happen more often and if it continues I'll try the powered USB port out. 
You might have simply been close to stall speed and pulling up too hard on the stick. This will cause the plane to go into a spin sometimes (which I guess could be mistaken for a calibration issue).
Keep in mind, this is more of a simulator than an arcade game... you can't simply jerk the stick around. You have to get a feel for what the plane is going to do, and use slow, gradual adjustments with the stick (just like real life).
Kind of like a race car.. you can't simply jerk the steering wheel all the way to the left at 200mph, and expect it to actually turn left on you!
