There is a known issue so please don't lock them down or put them on a vendor. You'll lose them.
From another post from Athos:
I think you all know about this bug through posts here, but I'd like to share this from EA Japan official site:
- Please don't lock down canon balls(light or heavy) or grapeshots(light or heavy) in your house( including locking down them through putting them into containers which are locked down )
- Don't putting canon balls or grapeshots into backpacks of vendors,
or you will lose the canon balls or grapeshots.
From another post from Athos:
I think you all know about this bug through posts here, but I'd like to share this from EA Japan official site:
- Please don't lock down canon balls(light or heavy) or grapeshots(light or heavy) in your house( including locking down them through putting them into containers which are locked down )
- Don't putting canon balls or grapeshots into backpacks of vendors,
or you will lose the canon balls or grapeshots.