JoshyPHP @Toby was saying (in Gitter) that mod_rewrite is necessary ATM, so that would probably by why.
He also mentioned that @Franz may be planning to rectify that in the near future.
EDIT: Ah, yes, here it is in the installation instructions:
System Requirements
- A web server: either Apache (with mod_rewrite) or Nginx
So it seems Lighttpd is off the menu for now. (It also rules out the QNAP box I use for translation, so I feel your pain.)