When using the Rod of the Shifting Crust to place blocks, if you have less of the replacement block in your inventory than the blocks available to be replaced, you get 2 extra "phantom" blocks. I noticed when I made one petal block, then swapped a dirt block from a 7x7 dirt area. It replaced one dirt with the petal block, then put 2 extra ghost blocks, which reverted on a right-click with an empty hand. When I had 4 blocks (white wool), IIRC it seemed to put 6 out, 2 of which were phantom.

Confirmed in a barebones instance with just Forge 10.13.4.1469, Baubles, and Botania r1.7 211.