Hello! Sorry, I didn't clarify what I mean: first, stand up on the ground under water, then walk, and orient your view slighly down. You will be able to walk under water on the ground (everything happens on the ground), and if you start to sprint with hitting CTRL, the character should run under water, but, instead, he turns in swimming mode (but the behaviour of the model and the camera shaking acts like it should). If you can't reproduce, I can show you a recording.
Seems problem solved in 1.14.1 Pre-Release 2.