Sounds like it might be an issue of how your layers are set up. I had a similar experience when starting out, if you put the closed eyes on the same layer as your mouthshapes, they'll both display on the base model on top of it and can't display a mouth shape at the same time for some reason. Set up your base model so there's an eyes open and eyes closed version on the same layer for blinking then set up your mouthshapes on the layer on top of that.