zsh selects a pasted text

This feature was introduced with version 5.1 of zsh. You can disable it by unsetting the variable zle_bracketed_paste:

unset zle_bracketed_paste

Note: Aside from highlighting pasted text (which is, as far as I understand, actually done by the terminal) it also prevents ZLE from parsing special characters like tabs and newlines. This means for example that if you paste multiline text, zsh will not automatically (try to) run each line as if it were a command, instead the whole text will be pasted as a whole with literal tabs and newlines.