I have just changed from DS 4.8 to DZ 4.9 and there is one difference I find annoying. In 4.8 when I opened the windows at the side of the viewport, the viewport shrank to fit the space between them, and the viewport controls in the top right of the viewport remain visible. In 4.9, the side windows overlay the viewport, obscuring much of the viewport and the viewport controls. Is there any way I can set 4.9 be the behave the same as 4.8

That's a known glitch in 4.9. There are a few ways you can fix it, till they get round to fixing it properly. I switch from the Viewport tab to the Shader mixer tab, then close and open the right hand pane, (Mine is the Parameters pane). That fixes the resizing problem for all the tabs and I can switch back to the Viewport.

Close the Shader Mixer and Shader Builder panes - you can do this by right-clicking on their tabs and selecting the Close pane option.

Sorted Many thanks