For the past several days, I've not been able to store milk outside of my hotbar and even there is only lasts as long as I walk.  When I try to move it to my hotbar storage area, it immediately empties.  If I run, jump, or swing a weapon while it's in my hotbar, it empties.  My brother plays on his cell phone and we are in the same Realms Club/world and he has been experiencing the same glitch I am so it's not specific to me.  

It's become a major inconvenience in the dessert and snow biomes and in battling the pillagers and defeating the Chief (Banner).