Why is my rotate animation all wonky when applied to an Activity transition?

But when I animate an activity transition instead, something entirely different happens. The activity starts to rotate counterclockwise, but at the same time it flies off the top right of the screen. Then it comes back, still rotating counterclockwise and by now upside-down, and flies off the bottom left of the screen.

Finally, it comes back and ends its rotation upright. No matter what I specify for pivotX and pivotY, the behaviour is always the same. They seem to be ignored completely.

And either way, the thing is certainly not rotating around any fixed pivot at all! What kind of nonsense is this? Is it a bug?

For completeness, I saved this animation as res/anim/spin. I've put together a minimal Android project that demonstrates the problem. Here are the ZIP file with the project source and the runnable APK file.