Since the 1.10.0 update. If you mine a big mushroom with a silk touch too you doesn't get mushroom blocks with all sides red or brown like usually. You'll get them with the pores texture on all sides.

“Red mushroom blocks” and “brown mushroom block” are also not stackable even though they look the same.

This bug occurs in Single Player and Multiplayer (Realm).

I don't know if the Block IDs did change for the mushroom blocks but if so then it could have caused it.