Static plane not infinite with Soft Bodies

[chamfer]

I hope this isn't anything too simple, but it's been giving me problems for a while and I don't really have much experience with Bullet. I've set up a scene with a soft body sphere rolling along a static plane. The sphere can be instatianted anywhere on the plane and will collide and start rolling, but after a small distance (pretty much always the same distance) it will fall as if the plane has ended. With a rigid body sphere this doesn't happen. Changing mass/vertex count/time steps etc has no effect on how far it travels before it falls off. Any help greatly appreciated!

[Edit: Guessing it's something to do with the soft body's bounding box (not sure if the right word!) being updated in the world]

[chamfer]

Seemingly solved. I call world->contactTest(softBody, resultCallback) every frame and for some reason that has fixed the problem.