You can not open the inventory of a redstone component that is currently being updated by redstone. 

Steps to replicate:

1. Fill the inventory of a redstone component (for example, put nine stacks of bonemeal in a dispenser).
2. Repeatedly power the redstone component (for example, using an observer clock).
3. Attempt to access the inventory of the redstone compenent (for example, to add more bonemeal to the dispenser).
4. Fail to open the inventory and resort to turning off the power so that you can access the inventory.

Expected Outcome:

You can open the inventory of the block any time after it has been placed in the world.

Actual Outcome:

You can only open the inventory when the block is not being powered.