I have the same situation with my dd when she returns home to me. But it is only if the sm is there. She looks really shifty and unsure what to do with herself, so whilst she hugs her sm, she is otoh 'cold' towards me. She is 8 but this has been happening for years.
I am OK with it now because I think she is confused and finds it hard to know which role to take on when we are both present. The main thing for me is that when we get inside she is back to her normal self and hugs me loads 
WRT to mummy thing. I do think this is really not on, and blame your ex dh for this the most. My dc call their sm by her name and their sd (my dh) by his name. None of us would have it any other way. She is not her mummy. She has one of those - me. Likewise, she also has a father who is present in her life a lot, sd does not need to be 'daddy'.
It is all very well to say well at least she likes her, is happy with her and that is the best thing for her, so therefore it is OK. But these things can all take place without her being referred to as mummy. It would seem, because of the smirk thing, your ex is revelling in her doing this because it makes you uncomfortable. That, along with the grandma, brother, aunty thing would make me really cross with him tbh.
I'm sorry, but I would really try not to let this happen. I would gently encourage your dd to call her sm by her name and every time she says mummy about her, just remind her.
Bloody tough, but you sound like you are doing everything you can in a kind and loving way.
I second everything chelen said too.