After vassalizing an empire, my armies in their territory are marked as trespassing creating a grievance.

Also, my armies can't enter my vassal's territory once they exit.  This is strange behavior for a vassal to enforce closed borders with their liege.

Experiencing same issue right now in my current game.

This is the case when the vassal has made his demand on you. Then the trade routes are blocked as well as you cannot enter his territory.

paxis76 wrote:

This is the case when the vassal has made his demand on you. Then the trade routes are blocked as well as you cannot enter his territory.

No, this is not the case. In the example I mentioned, this bug occurred immediately after vassalization and there were no demands.