I'm not sure if this is completely correct but, when i've been making custom scripts I put them in share/raw/scripts/custom and it reads them fine there.
Could be that it only reads from the raw/scripts and not usermaps/zm_mapname/scripts.
The weird thing is that even changes to the raw/scripts one doesn't change anything
I'm having a similar problem with a different script (_zm_pack_a_punch.gsc). Even just adding a few simple "iprinln" lines won't appear when running the map.