I appreciate your efforts, but it's not enough to fully support UNC paths.
We still have par2-classic in the SABnzbd distribution because par2-tbb contains several errors.
When they occur, we silently run par2-classic instead.
In fact we're looking at using an alternative for par2-tbb, called phpar2.
Also, using UNC paths suggests that the "incomplete" folder could be placed
on a networked drive, something we recommend against due to the heavy network strain.
You could help us by giving your opinion about the merits of phpar2 vs. par2-tbb.
(BTW, I suspect phpar2 also doesn't support UNC).