How to reproduce:

1. give yourself a command block
2. place it down and make it a repeating command block that is always active
3. type in the command block: item replace entity @p container.0 with [any item e.g. sand]

When you throw the item using Q, the item seemingly dissapears

However, you can still keep throwing the item from your inventory even though it looks like its not there

You can also place it like normal

When you go into your inventory, you cannot pick it up like a normal ghost item