This may or may not be a bug. Maybe it's intentional.
If a hostile fox attacks you and you run back to a ring where foxes are normally non-hostile, and then you go inside a building and come back out, the fox will no longer attack you on sight. Presumably by being trained* back to a 'safe' ring, the fox has become non-hostile in general. This seems like it might be a bug, except that I could see how it might be intentional, because it would probably be a Bad Idea to let people train* hostile level 50 Mordor foxes to Brodgar and leave them to butcher newbies.
I'm also curious whether the fox's combat skill is a variable on the fox, or dependent on what Ring it is in.
I suppose the most carebear position would be to degrade hostile status as it is now and to make combat skill dependent on the Ring the monster is currently in, resulting in deadly foxes trained towards newbies losing their deadliness.
The harshest position, by contrast, would be the opposite, which would mean that you could never flee from a landcarp and expect to be saved by running into a safer Ring, but which would also mean that you could use landcarp as an army against your enemies (which would be cool), or newbies (which would not be cool). This one would probably fit better overall with the feel of Haven & Hearth so far.
* train = MMO terminology for leading a monster or monsters to a destination.