[Xmonad] shellPrompt kills xmonad

Hi, I've got an issue with the shellPrompt extension here. Everytime I'm entering some keys in the shellPrompt xmonad crashes. Sometimes it crashes after the first pressed key (e.g. 'a') and sometimes after the second key (e.g. 'c' than arbritrary letter). However it does not crash, if I open the shellPrompt and exit it by hitting ESC. I only notice this behaviour on NixOS. The same config is working on debian etch without crashing.