Pasting certain unicode characters into an edit window results in MySQL2 error

If you copy the character 𝕊  from some nlab article (for instance the one on Spec(S)) and paste it into some other article's edit window (outside of a math environment), you'll get a long yellow error message starting with 

Mysql2::Error: Incorrect string value:  '\xF0\x9D\x95\x8A) ...' 

This will also happen for the character 𝔸 but not for ℚ.
