When the borders first expand (or an outpost is built) to make the connection, it always seems to wait until the next turn to recalculate the unrest.  I believe I've seen it take 2 turns to do so on occasion also.  I haven't ever noticed it reverting, I'll start looking for that.

I think I have noticed this when I load a saved game as well.  I'll try to catch it next time.

I have a save game, in 0.91, where I have a territory which is not contiguous with capital. But since Publius also provided one, maybe mine is not necessary?

My issue arose, I think, because when I planted my outpost between between my city and my capital the territory of that city did not quite reach the outpost. A few turns later it expanded a square and should have made the connection, but did not. (I noticed the issue much later.)

Edit: the above report is old, so maybe my save illustrates a different issue?