Well, it turns out I was a sloppy betatester

After playing around with Casse a bit I loaded the old savegame and tried to pass to the next turn without activating the script - and to my great surprise, there was no crash. Since all the CTDs I'd had before were unaffected by the script I'd not thought about it this time. I re-loaded again to verify this, and the script is definetly what is causing it.