/more cannot change itemstack for items like potion / bed to 64

CMDBOOK-2433 - Reported by PikachuEXE

I was using /more AdminCmd in Spigot 1.7.10, and my server has recently upgraded to 1.8.3 and changed to use this plugin.
As mentioned in Summary, items like potions or bed cannot change item count to 64 with /more
I cannot use WorldGuard's /stack to do that, since I have some custom potions

Is this intended or a bug?