My MLC/WW has been doing this for a long time. She no longer rides in the front passenger seat with me. I don't really think of it as childishness. It's not done in a calculating way. It's not done to make a point or to send a signal. I believe she does it because she's a very visceral, intuitive animal, and she just cannot bear to be that close to me right now, when her mind is set on leaving me. It's part of the MLC package: no eye contact, etc. I think close contact disrupts the world she's created in her head about me.
Me: 50, MLC/WW 45 Young kids Nov 2015: BD1 Apr 2016: BD2 Jan 2017: W filed Feb 2017: D final