[Freaky]

Escaped here. How are you configuring your completion?

    -% zsh -f
    voi% echo $ZSH_VERSION
    5.3.1
    voi% autoload -U compinit
    voi% compinit
    voi% git checkout <tab><tab>\$\(./pw3n\)
    Already on '$(./pw3n)'
    Your branch is up-to-date with 'origin/$(./pw3n)'.
    voi% git checkout com<tab>plete_\$\(./foo\)
    Switched to branch 'complete_$(./foo)'