Sorry for the large delay.
Bullet can do continuous collision detection between sphere versus 3d polysoup (terrain), by creating a 'temporal AABB', and then doing CCD between sphere versus each triangle that overlaps with this temporal AABB. This temporal AABB encloses the full motion (begin, in-between and end position) of the sphere.
This feature used to be working, but the CCD feature hasn't been activated in recent releases. When I get back to enabling CCD response (using time of impact), I'll doublecheck this is working properly.
Thanks for the feedback,