OK, I dug deeper into it. I believe you are correct - this appears to be a ParaView bug.
The way I tested this is that I used filter clip, then clipped off a small side of your data. This converted your data to tets, and it works correctly. It also works correctly if you run the tetrahedralize filter on the data before the pyhon calculator.
I have reopened the bug. Thanks for this bug report - it is well done.