Why would this be weird?

My dad's coming to my mom's house for Christmas.
Ordinary parents do this all the time; of course, they tend to be married. To one another.
My parents have been divorced for 30 years.
My mother has not always been kind and gracious, particularly to my step-mothers (there have been 2; Bobbi died in September. She and Dad had been married almost 17 years).
She called to talk to me about when everyone will be arriving at her house on Tuesday, and seemed shocked that I suggested that Dad might not come until at least one of his children had arrived. "Why would you think that?" she said.
Gee. I don't know.
(what's the emoticon for sarcasm?)

It promises to be a good time, except for the occasional weird moment. Jamie the Exceptional will be there, and she'll be the belle of the day. So we'll just see...