Cannot sneak on shulker or boat

The player doesn't perform the sneaking animation while standing on a boat or a shulker,
The player is also very fast whilst sneaking & walking on them, it also works in adventure, survival & creative mode.
This is a duplicate, but i only saw it on older versions, and it seems to work in 1.15.1 pre-release 1, which i've not found a report about in this specific version.