I get reproductible zsh crashes. Steps:

1. Start zsh 5.1.1 with default config of prezto enabled
2. Write/paste :prezto:module:editor:info:
3. Move to beginning of the line, type zsty<TAB>
4. autocompletion takes a very long time. C-c
5. zsh shows next prompt dies with segmentation fault

I re-compiled zsh with debug info and attached a quick gdb log of the
coredump. Unfortuantely, I can't reproduce it under valgrind. Running
zsh with a small plain .zshrc also results in no crash.

As I'm not very familiar with zsh I don't know what else to
test/provide, feel free to ask for more info.

Happy hacking!
-- 
Bart Polot