[This is a minor bug that involves crafting. If you place your cursor over the inventory slot where the completed item will be placed before the item is completed, you will not be able to take the item until you move your cursor to a different slot then back again.]
Steps on how to reproduce issue:
Leave the first slot of the crafting station open
Start a single stack item crafting
Place your cursor over the 1st slot
When the item finishes, it is placed in slot one, and you are unable to take it until you move to another slot, such as slot 2, then back again.
I assume in step 4 you mean move the cursor to another slot then back? If so this happens any slot where the newly crafted item will spawn, even if the inventory sorting is set to something other than custom.
For example if in my inventory I have branches in slot one and all my crafting ingredients in other slots if my cursor is on slot 2 (where the item will spawn) I will have the same issue