Item flow speed in upward bubble columns inconsistent with flow speed of other entities

Upward bubble columns created with soul sand show inconsistent flow speed of items compared to other entities: Items rise about twice as fast as in normal water, while other entities like players, mobs or xp orbs shoot up pretty fast. This inconsistency makes item elevators kinda slow, while everything else can be transported upwards very fast.
Downward bubble columns made with magma blocks still drop everything, including items, very fast and therefore work consistently.