Minecraft Username: @y0landi Brief Description: Whenever I pick up an item and my selected item slot is the slot the item would be placed in, it skips that slot. My inventory is also empty. Instructions: No clue... sorry just thought this needed to be known. How many times did you recreate this bug?: Once but the effects are reoccurring Result: My first item slot is empty, I pick up an item, it goes in my second item slot instead of the first. Expected Result: Whenever I pick up an item, it gets put in the first empty item slot. Evidence: Thank you @a_man21 for checking my inventory is empty.
Try an unmodded client. If this doesn't happen with a vanilla client it's very likely that your client or macros are at fault here.
