CTRL+pickblock overwrites selected item

In the new snapshot, the feature to ctrl+pickblock blocks to copy their nbtdata was added. however, when i tried it it overwrote my current holding item.
What i expected to happen was
the item would assign itself an empty slot in my hotbar
What happened was
The item overwrote the sand block i was holding.
steps to reproduce
1. hold an item.
2. Place a block with NBTdata
3. CTRL+pickblock the NBTdata block
4. The block overwrites the block you are holding