This problem can be caused by several things. Once you get airborne, level off and turn on auto-level (X key). See if that pops off too. If it does, add additional dead band. I set mine about 1/4 inch from the bottom. Add an equal amount of damping.
If it holds auto-level, than it must relate to something you are doing on the takeoff run. Keep your feet off the pedals during the takeoff, in fact don't touch any of the controls.
If that doesn't fix the issue, you are carrying some control surface displacement somewhere. Double check the stick, pedals and throttle in Windows and make sure the input cross is centered. Double check trim mapping too. Check and see if any piece of your hardware is spiking when centered.
My regards,
Widewing
