Okay, I just took a look at your .cap... and it is working.
It just looks like it's not.
What's happening is your physics goombas are getting stuck on the pipes. They're trying to turn around, but they can't.
Try changing the goomba's physics settings like so:
Linear Dampening: 0
Contact Friction: 0
Contact Elasticity: 100
World Friction: Exact
World Solver: Exact
You will see that the goombas do have a mind of their own. They still get stuck, but not as much.
I think the reason they weren't breaking loose of the pipes until the other goomba hit the pipe is there was a transfer of force through the objects that was big enough to knock it free. Which is strange, because the pipes and ground are set to Immovable. I don't really understand it.
Anyway, it's all just a byproduct of trying to use physics for a platformer. Theoretically it can be done, but it's a weird use of the physics engine. And if it's a weird use of the physics engine, you're going to get weird results. My recommendation is that you stick to non-physics behaviors for tasks that don't need physics.
And yes, I understand that you want to use physics because it's easier... but in practice it just isn't easier.
Set alterable value
What is this MMF crap? gbt dailyclick