De README
Incompatibilites between 5.0.8 and 5.1
The default behaviour when text is pasted into an X Windows terminal has changed significantly (unless you are using a very old terminal emulator that doesn't support this mode). Now, the new "bracketed paste mode" treats all the pasted text as literal characters. This means, in particular, that a newline is simply inserted as a visible newline; you need to hit Return on the keyboard to execute the pasted text in one go. See the description of zle_bracketed_paste in the zshparams manual for more. "unset zle_bracketed_paste" restores the previous behaviour.