Pressure plate release time is not consistent as measured from the time the last entity moves off of it

Steps to reproduce

1. Load pressure plate test world.mcworld.
2. Press the button on the "1 Item" command block, and watch the scoreboard.
3. Press the button on the "2 Items" command block, and watch the scoreboard.

Expected result

The scoreboard times in steps (2) and (3) should be different by 8, because the second item enters the pressure plate while the first item is still on the pressure plate, and it leaves the pressure plate 8 ticks after the first item leaves the pressure plate. In general, a pressure plate should always continue powering for 20 ticks after the last entity leaves its detection area.

Observed result

The scoreboard times in steps (2) and (3) are both 40. In general, a pressure plates always powers for a multiple of 20 ticks from the tick in which the first entity enters its detection area. It stays "on" until the last entity leaves, but then turns off at the next multiple of 20 ticks from when it first turned on instead of at 20 ticks after the last entity leaves.