I've routinely had non-aggression pacts, peace treaties, and alliance produce an expired message 1 turn after I signed them. For example, the turn after researching alliances I signed an alliance with the next three largest kingdoms only to receive the "Alliance with xxxx expired" message on the next turn. However, under the kingdom report screen it shows all three to still be my allies.
The two images below are from the same turn in the same game.
