Item number in off-hand does not update when consumed and picked up simultaneously

Set-up:

With a stack of food in the off-hand (tested with rotten flesh and golden apples), and an otherwise full inventory, stand over a pile of the same item as is in the off-hand. Repeatedly eat from the off-hand.

Expected behaviour:

New items are picked up as they are consumed, and so the stack remains full. Food can be consumed infinitely.

Actual behaviour:

Number of items in the off-hand gradually decreases until it is empty. The held item in the off-hand and in the off-hand HUD slot disappear, and food can no longer be consumed. At any stage, even after the off-hand is visibly empty, and when not standing over the pile of items any more, disturbing the off-hand will cause it to become refilled again. This can be done either by swapping between the off-hand and main hand, or by clicking on the slot in the inventory.