Certain plants cannot be placed underwater

Certain plants can be placed underwater, such as Leaves, Vines, Lily Pads, and Dead Bushes, but others cannot. Be consistent, please. This is ridiculous. 

Certain plants include:

   -Saplings of all types 

   -Cactus

   -Sugar Cane

   -Farmland/Crops/Stems

   -Flowers/Double Flowers

   -Nether Wart

   -Chorus Plant

   -Mushrooms

   -Fern/Large Fern

   -Grass/Tall Grass

   -Bamboo

   -Cocoa Beans