I'm trying to design a few things in my creative world before building them in my actual world.

While I'm trying to fill up the dispensers with bone meal as quickly as possible, the game will click on the item that the cursor is pointing at (always the fifth slot from the right, in the top row of the inventory screen), when the menu pops up; causing me to drop whichever item when I press esc or e to back out of the dispenser/dropper menu to fill up the next one.