Vassals not fabricating claims?

[zenisar]

That might have something to do with the HRE though.

I catch and release Guyenne, ever game, even as Byzantium, and they claim every French province they border, France is normally my rival by then though, they keep claiming them and reclaiming as they fade.

There might be some link to HRE indeed just did not figure out yet what it is. However, I also noticed that some of my HRE vassals refused to accept to take a neighbouring province for free claiming that "This province is part of HRE and Bohemia (= the giving party of the transaction) is the emperor." While Guyenne freely receives neighbouring French provinces even they had no claim or core on it.