Items floating at the top of the water sometimes seem to float above the water's surface

The Bug

When items are floating at the top of the water, sometimes they seem to float above the water's surface for a second, then sink down a couple blocks.

Steps to Reproduce

• Throw an item into some water.
• Wait for it to reach the surface of the water.
• Look closely as the item entity moves up and down.
• Take note as to whether or not item entities floating on the surface of liquids appear to be always touching the liquid.

Observed Behavior

Item entities floating on the surface of liquids don't always appear to be touching the liquid.

Expected Behavior

Item entities floating on the surface of liquids would always appear to be touching the liquid.