Physics bug?

Hi. I am seeing strange behaviour in a simple project I have made.

My setup is as follows:

The blueprint script is very simple:

And the final piece. This just flips the model 180 degrees (makes it point in the opposite direction). This works fine. But after a second, when I re-enable the physics, my model flips back to its original rotation, and moves in the opposite (original) direction again!

I have made a video where you can see what happens:

Is this a bug, or am I missing something?