Minecraft Username: FuriuosGeorge Brief Description: if you strip the cap of a giant shroom and then wack the stem with any of the treefeller modes of the magic axe you get no drops Instructions: strip the cap off of a giant mushroom switch to a treefeller mode on the magic axe hit the stem How many times did you recreate this?: about 6 Result: no drop, and nothing magically put in inv Expected Result: something. either brown or red mushrooms or just the stem blocks themselves since a shroom type can't be determined for the stalk. Evidence: none to provide, but I suspect the magic item code is looking for a cap to be touching the stem to determine what to drop.
This is how vanilla minecraft works. The Minecraft wiki states that Mushroom stem does not yield the mushroom drops - only the caps do.