I'm using UltraVNC Viewer 1.2.2.3 on Windows 8.1 x64.
I have set the viewer scaled by 90%. When I connect to the server the first time, I get a window that shows the entire screen of the server. So I can see the full screen of the server without running the viewer full screen.
If I minimize the window, then restore it, I get horizontal and vertical scroll bars to pan the server screen. If I expand the UVNC Viewer window horizontally, then I can see the entire server screen without scroll bars. If I minimize the Ultra VNC viewer again and than restore it, I don't see all the server screen and get the scroll bars again.
Another user reported this in 2016: http://forum.ultravnc.info/viewtopic.php?f=71&t=31824