When engaged to a villager, they can become engaged to another villager as a part of story progression.

Attempting to use divorce papers returns: I am not married to anyone.
Attempting to use engagement ring returns: interaction.engage.fail.engagedtoother
Attempting to use wedding ring returns: It's a pretty ring but I'm already married to you, silly.

Also, any children with said spouse show me as the father, and none as the mother. This is with story progression set to 1. It's happened to me at least 3 times now on different worlds. It usually takes within 5-15 days in game (rough estimate) but it removes a lot of functionality as you cannot divorce, do spouse specific interactions, or remarry.

Using MCA 5.0.4