Yeah... just because an aquatics store sells them doesn't mean they know their butt from their elbow when it comes to fully submersible versus partially sumbersible versus bog plants.
For instance, they were selling mare's tail and some other plant at Lowe's here in town as an oxygenating plant, but they had it completely out of water. They were selling their water lilies this way as well. They have them in aquatic cups, but they have everything filled up only halfway. I wonder how many plants they lose when they do stupid stuff like that.
I've heard people say that dumbcane arrowhead plants can be used in aquariums. The only way you can add dumbcane or arrowhead is to thoroughly rinse their roots and have their roots in the tank, NOT the whole plant. But that didn't stop my LFS from assuming aquatic means 'under water' and fully sumberging hers. It rotted after a few weeks.
Technically, dumbcane should NEVER be used with fish in any shape, form, or fashion. The properties of dumbcane that numb the gums and tongue are tiny crystals that, as the roots and leaves break down in the water, are released into the water the fish breathe. It'd be like living in a house full of shredded fiberglass... O__O;;