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Description of problem:
zsh exits with "parse error near `!'" for script with unescaped ! character

Version-Release number of selected component (if applicable):
zsh-5.0.2-19.el7.x86_64

How reproducible:
100%

Steps to Reproduce:

$ cat simple.ksh 
#!/bin/ksh

if [[ -z $(echo !) ]]; then
  echo this does not happen
else
  echo ok
fi

$ zsh simple.ksh
simple.ksh:3: parse error near `!'
simple.ksh:4: parse error near `$(echo !) ]]; then'

with ksh linked to zsh, to invoke zsh in posix mode:
$ ksh simple.ksh
simple.ksh:3: parse error near `!'
simple.ksh:4: parse error near `$(echo !) ]]; then'


Actual results:
Script exits with error: parse error near `!'

Expected results:
Script runs fine

Additional info:

Affected:
zsh version 5.0.2-19.el7

Ok:
zsh up until and including 5.0.2-14.el7,
zsh-5.0.8-8.fc22.x86_64 in fedora22

This issue seems to be limited to the $( ) notation, as the following script runs fine:
$ cat simple-ok.ksh 
#!/bin/ksh

if [[ -z `echo !` ]]; then
  echo this does not happen
else
  echo ok
fi

Also AT&T ksh runs this script fine.

This seems to be yet another regression introduced by the fix for bug #1241023.  git-bisect points to the following (non-trivial) upstream commit as the fix for this bug:

https://sourceforge.net/p/zsh/code/ci/cfd91eac

Created attachment 1160672 [details]
[PATCH 2/7] Resolves: #1338689 - better initialize parser state

This fix is isolated out from a huge upstream commit that includes major
code refactoring changes together with the initialization fix actually
needed to resolve #1338689.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2016-2152.html