Testing again, now that I know my password manager is 
safe. The same thing happens now: enough emoji to get a green “okay” is not enough to actually work. And as I tried longer and longer passwords, iteratively, it logged me out, I think on the third try. When I did successfully set it, to a 
emoji password, I still got a “you have been logged out” message flash by, but it didn’t actually log me out.
Not sure if that log out thing is an emoji-specific bug or some sort of misguided (or at least unhelpful) feature. If it is a feature, please make the “you have been logged out” box explain why.