Verification builds: 1.2.13.5

Summary: If you have a block with data in your hotbar, then pick a block of the same type with the middle mouse button, the picked block will overwrite the block that was already in your hotbar.

Impact: Harshly impacts the workflow for any project involving command blocks or redstone, making it much more tedious to copy blocks without accidentally deleting them.

Repro Steps:

1. Give yourself a command block and place it on the ground.
2. Write some text in the command block.
3. Pick the command block + data (ctrl + mouse 3).
4. Change your selected hotbar slot and pick the command block without picking data.

Observed Results: The command block with data will be overwritten by the new one.

Expected Results: The command block with data should be unaffected, and the new one should be added to the selected hotbar slot.

Screenshots/Videos attached: No

Notes: N/A