There is a known issue in ZSH, specifically versions up to and including 5.3.1, where a static pattern buffer is used in the history isearch.  However, the assumptions that led to this code forget that ZLE hooks may call other pattern functions as well, breaking functionality.

As an example, this issue breaks certain uses of zsh-syntax-highlighting (https://github.com/zsh-users/zsh-syntax-highlighting/issues/407)

A backported fix has been applied by both Arch Linux (https://git.archlinux.org/svntogit/packages.git/commit/trunk?h=packages/zsh&id=0e7db42263c914ae4c7b3c74df1e6c756c94fe8b) and Debian Stretch (https://anonscm.debian.org/cgit/collab-maint/zsh.git/diff/debian/patches/cherry-pick_48cadf48_be_more_careful_with_pattern_allocation_in_history_isearch.patch?id=348c47bdc3b6a92558d82086d168e7829437388a)

Both of these come from the original patch shown here: http://www.zsh.org/mla/workers/2017/msg00034.html / https://github.com/zsh-users/zsh/commit/48cadf48ff9c61ce09e826ad9a58e250e999a262

I am hoping that Fedora would also be willing to provide the same backported fix.

Version-Release number of selected component (if applicable):
zsh-5.3.1-5.fc26-x86_64

Steps to Reproduce:
% bindkey '^R' history-incremental-pattern-search-backward
% evil_hook() { a=(); : ${a[(r)foo*]}; };
% zle -N zle-isearch-update evil_hook
% echo "foo"
% echo "bar"
% echo "baz"

type: <^R>b
% echo "baz"
bck-i-search: b_

type: <^R>
% echo "foo"
bck-i-search: b_

'foo' is found instead of 'bar' because evil_hook modified the static pattern used in isearch.