The way cave story is made, it does a <AMJ for the fireball (Checks for it) in order to make chako say "go for the jellies".
But, I didn't the fireball.
I got a missile upgrade where santa would give you the fireball. Meaning yeah, it would go to Head.tsc, not finishing the script.
Oh what? That's weird. That shouldn't be possible anymore! Will investigate!
Whelp. My intentions were in the right place, but a bug with a frankly moronic cause was causing the items flagged as "never swap this with missiles" to instead act more like "never swap this with lipstick/panties/life pot". This is fixed in v0.3.