Automatic Gain of Provinces as the Emperor

[Time Commander Bob]

I am playing as Austria and am the Holy Roman Emperor and since about 1425 I have often gained provinces off other member states without doing anything nor am I informed of acquiring them other than seeing that I have unlawful imperial territory and revolt risks. These provinces are always territories that other member states have conquered but do not yet have cores on. Why does this happen exactly, wouldn't a successful nationalist revolt result in them becoming independent automatically?

[Veliky Kaiser Theos]

I'm fairly certain that this is other HRE nations giving you unlawful land. If you ever play as a non emperor nation and take an imperial province, you will find that you are at some point you are given the option of giving the emperor the land and getting prestige, or losing prestige while keeping the land and the land gets the "unlawful territory" modifier.