I woldnt be quick to call it a scripting problem because its the identical script to my other ICS ROMS that DO work on twrp (Rezound and Evo 3D).
But who knows, I could be wrong. But generally speaking, if it works on one Recovery and not another then I would think the Recovery would be the issue and not the script.
I will flash this and test it myself and see what the deal is. The scripting I use with my ROM is pretty basic.
Format, mount, extract, symlink, unmount. Nothing fancy there.
I'll join IRC channel after I have to time to play to help T/S if OP wants?
EDIT: BTW: I love twrp and its always been my recommended recovery. I have been bugging Con24 who ported twrp to Rezound to do this for us so I am really happy to see twrp here!!!!!!