I currently play quark in a Minecolonies Modpack and my tamed foxhounds attack my citizens. The only way to prevent this, is by making them sit.
Is it intended, that the foxhound can still attack on his own, although he is tamed? I guess, the foxhound recycled code from the wolf/dog, which still attacks skeletons although it has been tamed. But in this case, this really is a pain. I guess there is only a if statement missing in the attack/target select goal of the foxhound, when tamed.

they're not attacking your citizens, they're trying to play with them. they just aren't aware that things that aren't from the nether aren't fireproof