Can a Protectorate block a trade route?

A nation that is my protectorate has one of those pirate flags showing up and they are standing on a land road that connects one of my cities and theirs. However I am still in "protectorate state" with them, so doing that didn't break anything, and also it still shows that the trade is successful. Is this a glitch where the game THINKS they want to be blocking my trade but actually aren't? It would be stupid to block a trade going TO them anyway.

They could be raiding the trade route of another nation that is using that same road.

Not sure of the pathfinding for road trade, but at sea there is only a few main "highways" of the trade route. You (or the AI) can plant a ship and raid the route even if it's used by 20 different factions and yet only be stealing from one.

It was definitely only ours. I moused-over the route and it showed it was only in use by me to them. So they were my protectorate but stealing from the trade we had established? Sounds like a glitch cause I don't think AI would want to do that.