1.1.3 collision bug?

So I was working through the Collisions tutorial that came with the new doc system, and I've discovered something rather wonky. If I follow the tutorial properly, when I set up the game to bounce the rock off the crate, it just hits the crate, and then shudders up and down. If I edit the bounding box of the rock however, all of the sudden the collision/physics work perfectly. I tried this again with a new object - I dragged another rock to the scene, turned on the collision receive/response, set the constant Y force to 100 and when it dropped onto the crate (which was set to BOUNCE but checked as immovable) the rock again got stuck and shuddered up and down. After creating a new bounds for it, things worked. Next I dragged another rock in, but this time instead of editing its bounding box I instead edited the box's bounding box (which up till now had not been tampered with) and this rock bounced perfectly without me having to first tamper with its bounds.

Perhaps this is a bug in the way TGB automatically generates bounds around newly created objects?