Overriding collisionShape attached to btRigidBody

[luxman]

Hi,

I'm able to create different collision objects like boxes, spheres and cylinders in bullet. But i'm facing problem with collisionMesh and probably my collisionMesh(btBvhTriangleMeshShape) acts as ground to collide with boxes and spheres.
Initially I have created a rigid body by passing sphere shape. Later on in a separate function I have created the collisionMesh(btBvhTriangleMeshShape), and freed the memory allocated for previously created rigid body and recreated it by passing collisionMesh. After running the application i have noticed that, if I made to fall objects on the ground, they detect the collision mesh at someplaces and fall into the ground at someplaces.

Am I following correct procedure to overwrite the collisionShape attached on a rigidbody?
Should I use btCompoundShape? ( I tried that but failed )
What would be the optimized solution for this?
Is there any example related to this in bulletDemos??
Please suggest me something.

Thanks in advance.