Holding the SHIFT button while running underwater does not make us crouch;
However, by holding SHIFT, running and then releasing the shift button, we remain crouched, even if we also stop running.
The mistake just to press SHIFT again.
Please, fix. ;-;

Video examples:

1) In this video I activate the swim mode and try to hold SHIFT, but there is no result.
Desktop_1.mp4

2) In this video initially I hold SHIFT and then activate the swim mode, getting result. But when I release the shift and stop running, I keep crouched.
Desktop_2.mp4