Not sure it's the right place to report bugs, so redirect me if I'm wrong)
Playing as Mongolia, was helping in a war my ally (Commonwealth) against half of the HRE, and he somehow got the idea to force everyone to become my tributaries (thx for 150 AE for no reason, but it's not the point).
So first he forced tributary on the emperor (Bradenburg), so the emperor got changed and I was able to start another war vs member of HRE (Brabant).
And that's where the weird thing happens. Commonwealth forces tributary on 3 other counties (Bohemia, Hesse, Silesia, at slightly different times, but within a year probably), and all of them automatically join my other offensive war vs Brabant. I also was attacking Ming at a time, and they joined that war as well.. They actually participate in the war too, not just showing up in the overview screen. Bradenburg still didn't join though, so I guess it only happens when an offensive war is ongoing when tributary is forced.
Below are some screenshots to demonstrate the situation and the save file (unfortunately didn't think to make a copy right after it happened, but the war with Brabant is still going, so you can see tributaries in an offensive war).
P.S. version is 1.22.2.0

Playing as Mongolia, was helping in a war my ally (Commonwealth) against half of the HRE, and he somehow got the idea to force everyone to become my tributaries (thx for 150 AE for no reason, but it's not the point).
So first he forced tributary on the emperor (Bradenburg), so the emperor got changed and I was able to start another war vs member of HRE (Brabant).
And that's where the weird thing happens. Commonwealth forces tributary on 3 other counties (Bohemia, Hesse, Silesia, at slightly different times, but within a year probably), and all of them automatically join my other offensive war vs Brabant. I also was attacking Ming at a time, and they joined that war as well.. They actually participate in the war too, not just showing up in the overview screen. Bradenburg still didn't join though, so I guess it only happens when an offensive war is ongoing when tributary is forced.
Below are some screenshots to demonstrate the situation and the save file (unfortunately didn't think to make a copy right after it happened, but the war with Brabant is still going, so you can see tributaries in an offensive war).
P.S. version is 1.22.2.0