WTF moment. Does anybody else know a person that does this?

My mother has a very annoying character trait and I was wondering if anybody else encountered something like this before.

For example: She cheerfully congratulates me for getting engaged, then secretly whispers to my future mother in law (who I am living with and she only met my mother twice without any other contact) “He is young. He will change his mind.”

And another one: She says that she is proud of me making life changing decisions and that her son is growing up, then whispers to me that I am acting too adult like and that I am making fatal mistakes.

I can see that it could be a radical mood change but she smiles when she makes those comments and doesn’t change her tone. All she does is whisper it to me and others that are close to me. Which makes them all wonder whether she was joking, was being serious or if they misheard. Basically a massive wtf moment.

Does anybody else know a person that does this? Say one positive thing and then make a snide remark that seems to come out of nowhere without any visible mood change?