Sometimes blocks and items cannot be picked up, one of these cases is shown in the following video: https://www.youtube.com/watch?v=B-dC2Sw0-DE

• It seems to happen when the player is touching a block side
• the items are submerged in a water stream pushing them into a block
• This sight is often found when mining for obsidian using the water bucket trick to not have the items burn up.

When you step back a little bit you can pick up the items.

Since the bug seems kind of vague and I can't really well document it, I kindly request some more experimentation to what the exact cause of the bug is.

In any case, this bug was found in a legitimate vanilla world without cheats, when I noticed items weren't going into my inventory while I clearly had room for them.

I guess it might have to do with the pickup range for items, and the position of the items/player to somehow glitch up.