Watering cans only happends in between runs, not during a run... else your plants will die no matter what which beats the point of the minigame
So I assume some message checks went wrong to check if the can is full or not it will never get in that state, bcs that's how it works with the gricollers can as there is no other way to check it.
ya it does fill with lunars, I have always been using it like that on my main
So like I said, most likely something with message detection, will run my main on it and see what happends ^^
Enjoy!