Enemies are allowed to enter tiles occupied by me

Version 0.92, playing Mimots

My troops were a little late arriving at a contested node, but my survey ship was in time, so to keep the Drengin fleet from entering I moved my survey ship to stand on the tile. If the enemy had done that, I would have been unable to enter that tile without declaring war.

However, the Drengin just ignored my ship, and moved there anyway...

I know the AIs are bending the rules, but this seems to me to be crossing the line!