Comment 2 for bug 1073077

It would seem to me that this is a bug in zsh.
It is demonstrable like this:

ubuntu@quantal$ sh -c 'f="foo=bar"; echo ${f%%=*}'
foo
ubuntu@quantal$ bash -c 'f="foo=bar"; echo ${f%%=*}'
foo
ubuntu@quantal$ zsh -c 'f="foo=bar"; echo ${f%%=*}'
zsh:1: * not found

It is work-aroundable by escaping the '=' in the shell suffix match with a '\'. Ie:
zsh -c 'f="foo=bar"; echo ${f%%\=*}'
foo