I have been trying to create FPS player (character) in Bullet Physics

I tried to use btKinematicCharacterController with capsule ghost object but the player fall through the ground.

Any idea how do I get the player to walk on the ground instead of falling through it?

I resolved the problem by adding the line:

m_overlappingPaircache->getOverlappingPairCache()->setInternalGhostPairCallback(new btGhostPairCallback());

However, the player penetrate the ground a little bit and then move up to get rid of the penetration, which case the player to appear going up and down sometimes.

Anyone know how to get the player to be stable on the ground?