So I had an issue with the barrel where after I had put it down and filled it with 800+ cobblestone I couldn't retrieve anything. So I kept clicking and suddenly the item went away and the barrel was filled with air. Not sure what happened. I just tried to pick items out. (There was a wood pressure plate next to it so maybe a redstone signal went through?) A second barrel I had on top worked as expected. Good thing it was just cobble.

Edit: I realized my backpack was auto picking up the cobble. Whoops. Sorry it's not a issue.