Navel Trade route through City Ruins

An Ottoman City of Bursa was the single tile passage between a large lake and the ocean. They had a trade route (from another city) the passed through Bursa. Then several turns after I razed Bursa to the ground the cargo ship happily passed through the city ruins, and it would have gone back too, if I hadn't blocked it. The attached savegame is at the moment of the screen shot and will show the cargo ship moving (on the next turn) and then coming back a few turns later.

I also saw this in Maddjinn's video, Beyond the monument episode...
I've not tested this yet but guess the program might recalculate the route when it is renewed after 30 turn-life terminates.
Maybe the program was designed to update route on some events like war or pillage. But city-raze was not included in these events yet.