Inventory Full and Still Picking Up Items

To be clear, it affects version 0.13.1, but when I typed that in I was informed that it does not exist... That aside,
The problem I'm having is this: When I go to pick items up and my inventory is full, I pick them up and they disappear. This applies to anything I pick up. Seldom does the game prevent me from picking up items when my inventory is full; It does happen occasionally, but it is a rare occurrence.
There have been many times that I have been mining and not paying attention to my inventory and after mining diamonds, they are simply not in my inventory after I pick them up.