So I got bored and tried swimming to the big island off the southern coast of Cherarus (Solnitchny?).

There was a single smaller island before the big one with only a lighthouse. On the southern end of this island I entered the water (I think with my flashlight in my hands) and after moving from the standing to the floating positions, I was unable to move until I relogged.

Swimming back from the northern portion of the larger isle produced the same result (this time confirmed with my flashlight in hand).

Both times were near rocks (confirmed).

I'll try to reproduce this if you guys want me to.