Was having a similar problem as discussed on the "show your plate!" thread (perhaps I should have made a separate thread.. ).. where I was using "cheer" for the open mouth but when on the main portrait menu my face went back to "none"
It actually seems to remember the expression too (or however the emote works) since when swapping portraits you can see the expression fall off the face as it morphs back to "none" when chosen.
Someone else mentioned that OTHER points in the animation saved correctly but stopping at my chosen point in particular didn't work, as they had tested with it as well.
As an experiment could you also try the emote you were having trouble with and see if other points in the animation save?