Pasting unicode from external applications with mouse wheel on Unix

Question

On upgrade from Emacs 24.3.1 to Emacs 25.0.50 pasting unicode from external applications with mouse wheel appears broken.

I start emacs -Q and select e.g. title of https://en.wikipedia.org/wiki/Paul_Erdős wikipedia entry in firefox. However with mouse wheel I get

Paul_Erd\u0151s

where as with normal clipboard-yank works fine:

Paul_Erdős

Pasting the same with mouse wheel (aka <mouse-2>) from Emacs selection works fine.