In a water volume, I noticed that my client only sinks to just below the surface, then stops sinking. However, in windowed mode, if I Alt-tab away to another window, the client starts sinking correctly. But if i come back (i.e. click the client window, making it active) the player stops sinking again.
I tried this with OZ 5.5 and 5.6 and got the same results in both.
Update: The above was done by lowering the ground from zero to negative heights and putting a water volume at 0. When i leave the ground at zero, raising a few mountains perhaps, then creating a water volume above the ground, say at 300, this problem does not occur. However, the client does sink much more slowly when the window is in focus than when not in focus. So the problem is rather insignificant in this case, not that it was terribly serious to begin with
I also noticed some other interesting behavior regarding water volumes, specifically in very large zones with very few to no raised ground sections. I'll elaborate on that if it becomes a problem.