How to reproduce

1. Place a command block with the following command

clear @p stone 0 0 

1. Place a comparator and a redstone line as shown in the picture
2. Get a stack of stone in your inventory
3. Active the command block
   → Notice the comparator gives an output of 1 signal strength, while the command block output said it found 64 items to clear

Notes:

• This affects the `give` and `clear` command. Possibly more.
• It doesn't matter whether or not items are actually cleared