When you perform the /clear command on a player whilst they are attempting to craft, it can cause momentary visual glitches depending on the speed of repetition - the slower the more jarring.
What I expected to happen was:
A player to not notice that the /clear command is being performed - unless an item was removed from their inventory
What actually happened was:
Graphical crafting glitches that are very jarring for a player to work with - depending on the clock speed of the clear command.
Steps to Reproduce:
1. Build a redstone clock (Hopper-Clock makes it most noticeable)
2. Aim some redstone at a commandblock performing the following command: /clear @a 0 0
3. Attempt to craft items
Find attached a video clip that demonstrates the effect (first proving it's inventory only by placing blocks and using items)