UDK: Rigid bodies disappearing after collision Thread

I've made some test boxes in Maya which I've imported into UDK as static meshes. I've also made a custom material for these boxes.

Then I right-click in the map and select "Add UT Rigid Body: testpackage.mesh.test_block" to add the model to the map.

Now, playtesting (Play from here) work mostly without a problem. The boxes respond to physical input and have the correct texture and all that.
However, they disappear when colliding with other rigid bodies. They just seem to despawn - but they seem to leave their collision models behind (because I can see that the boxes collide with invisible objects after this despawning has occured.)

I'm not using any custom collision mesh because they are just boxes after all. Instead I've assigned the 6DOB simplified collision model to all of them. I also have the "continous collision detection" enabled.

Anyone know what's causing this?

EDIT: Video demonstration (Here you can also see my boxes bumping into invisible boxes (collision meshes of the despawned boxes))
Youtube.com

EDIT2: This problem applies to EVERY static mesh, even the ones comming with UDK.

Edited by: Nightshade