I am king of Ireland and I had a claim on the Kingdom of Lotharingia. I waited until the Lotharingia was in an independence war. I pressed my claim and won. Now I am the king of Lotharingia. The deposed king is now a duke and has most of the counties of Lotharingia in his personal demesne. I would like to imprison and then banish him. The button for imprison does not appear, and the revoke title button is grayed-out. When I hover over it the message is "cannot revoke titles of non-direct vassals" or something like that. When I look at his character screen I am shown as his liege. When I look at the independent map mode his lands are shown in my color. I am able to revoke/imprison his vassals (various mayors and bishops).
This seems like a bug to me.
This seems like a bug to me.