See screenshot below, using 8.1.7.255

Ah, I think I actually know the issue here- I'm holding onto references of all tank blocks with my current algorithm. This is luckily a very easy fix, I'll just change the references to use my hashable coordinate wrappers.

Fixed!

I built the dev version from the source and tried it with your fixed commits, I still saw the orphaned TEs in Opis.