Zsh segfaults with "${:0:}" and other combinations, see URL for further information. Patch has been committed to the Zsh CVS already, http://zsh.cvs.sourceforge.net/viewvc/zsh/zsh/Src/subst.c?r1=1.115&r2=1.116 Please rev-bump :)
Fixed in 4.3.11-r1. Thanks.