Japan in 1.8

[Hexmage]

As a side effect of this change in 1.8:

Fight for your Subjects
In an earlier dev diary, we explored a few of the new things you could do with your vassals. Furthering that theme, you can now fight for your subjects’ casus bellis. So if for example, if your vassal has a claim on a border province, you can now declare war on behalf of your vassal using that CB.

Japan as the Shogun can now declare war on Daimyos using other Daimyos claims, which results in unbalance in Japan. Since it is now possible for Japan to declare war on any Daimyo that captures another province, making it virtually impossible as a Daimyo to be a threat to Japan itself.
Now I haven't posted this in the bug forum because I'm not sure if it is a bug or working as intended.

 

[AurochsAway]

I'd be extremely dubious if it's WAD. Bug it. As it's all special governments over there, it should be simple to make an exception until Japan is united.