The problem is well explained below, in the Summary section and in the screenshots.
Steps to Reproduce
1. Have something in your inventory (must be at least 2).
2. Use the new function (or do it manually) of
3. Let the left (or right) click go.
4. Try to gather everything up pressing two times left click (using the new function). It does not work.
5. But if you place the block/item in the hotbar, it works without any problems.
6. It works (as seen in the screenshot) correctly.