Typing pipe character prepends with backslash

Question

I'm getting a weird and very annoying behavior in my terminal. When I type a protocol (i.e 'http:') then the pipe (|) character a backslash() is automatically inserted before the pipe character.

My test:
 type 'htt'+'|'             => 'ht|'
 type 'htt:'+'|'            => 'htt:|'
 type 'http'+'|'            => 'http|'
 type 'http:'+'|'           => 'http:\|'
 type 'http://foo.com'+'|'  => 'http://foo.com\|'
 type 'curl http://foo.com'+'|'  => 'curl http://foo.com\|'
 type 'curl https://foo.com'+'|'  => 'curl http://foo.com\|'

The same thing happens when I use 'ftp:' but not when I use 'telnet:'

Does anybody know what could be doing this?

This is my system: OSX sierra iTerm2 3.0.12 zsh 5.2 (x86_64-apple-darwin16.1.0) pretzo (https://github.com/sorin-ionescu/prezto)