If you look at the screenshot I provided, after going two blocks above the ocean the flying animation is correct and everything is perfect. However, when you pass the third block the flying animation goes back to the buggy animation. This does affect every space beyond the third block. The animation still doesn't work.
To recreate this bug, create a world with the seed in the picture. Find the nearest ocean and try this yourself.
The slow moving is intended. Works as intended.