Steps to reproduce

(can use Flying items tester.mcworld for convenience)

1. Make a soul sand bubble column several blocks tall with containing blocks around it, but no roof on top.
2. Replace one of the containing blocks with a collisionless, water-blocking block like button, open fence gate etc.
3. Throw an item through the opening into the bubble column.
4. Make a magma bubble column several blocks tall with containing blocks around it, but no roof on top.
5. Make an ice path with sidewalls a few blocks long coming out of the bottom, and allow water to flow out along the ice. Stop the water at the end of the ice with a collisionless, water-blocking block.
6. Drop an item into the magma column from the top.

Expected results.

In step (3) the item springs up out of the bubble column and then falls back down. In step (6) the item travels down the bubble column and along the ice path and then falls down off the end of the ice path.

Observed results

In step (3) the item springs up out of the bubble column and keeps going up forever. In step (6) the item travels down the bubble column and along the ice path and then keeps flying horizontally while drifting upward.