[Milhouse]

Well then I wonder why it works for like 99% of my library but screws up for like 10 episodes or so.
Funny thing is, that those duplicates just show to another episode of a later season.

To be honest, as this is core functionality, you'd stand a better chance of getting an answer to that question by posting a new thread in the General section. If someone submits a pull request with a fix that is likely to be merged upstream, I'll happily include it.

Or you could just rename those 10 episodes so that there is no ambiguity.