What I think I will do is put 'zsh --login' at the end of my .bash_profile, so if the half-baked Zsh 4.3 crashes then at least I won't lose the terminal or be logged out.
Of course what I'm after is the ability to have files with names like
ĉi_tiu_estas_dosiernomo_kiu_enhavas_ĉapelitajn_literojn
without creating too much confusion at the command line.