The bug
When you throw an item in between two opposite water currents, the item gets stuck there.
Also applies with armor stand and player
Screenshots
[media]as you can see when the item is in the exact location with no momentum, it won't get pulled in either way, although it's not perfectly in the center.
How to reproduce
dig a 1*4 trench, put water in two middle blocks, throw an item in the middle
Can confirm. Might be intended, but I would expect the streams to already move the player when the majority of the hitbox is in the water stream, not only when the full hitbox is in the water stream.