I right-clicked with no blocks selected in my hotbar and I could place dragon heads which were previously in the hotbar selection, but removed. Video below:
https://youtu.be/cOUQ3ULEQ6A

I'm pretty sure blocks should not be able to be placed if no items are selected in your inventory.

I don't know how to reproduce the bug. The steps I took to get to it were too specific for me to remember. The best I can do is show you what the glitch is.

I'm very sorry that I don't know the steps. The report is just so you're aware of it.