I tried making some Magma Crab pillboxes, but unfortunately they haven't fired at anything. Here's the setup:

Each crab is behind a fortification, with a retractable drawbridge to block line-of-sight if needed. I tried chaining some ducks in front of them, and some odd things began happening:
- Both the magma crabs and the ducks became "Terrified while in conflict"
- The ducks moved away from the magma crabs, as if trying to run away (but restrained)
- The magma crabs didn't appear to shoot, but the ducks quickly became Tired
- No combat notifications appeared, even though the ducks were apparently reacting to the magma crabs
- All of my magma crabs have the "Vision lost" tag for some reason
Either way, nothing at all seemed to happen. I later opened the gates and let dwarves walk back and forth in front of the crabs, but nothing happened then either.
Have I not set this up properly, or do magma crab pillboxes not work anymore? Thanks!