This is surely a bug:  in order to close, say, piano roll view, I have to go to the bottom of the screen and x the little box that says piano roll.  But the first of such little boxes is underneath the minimized soft synth which is minimized: so you can't get to it without maximizing the synth, then closing the piano roll, then re-minimizing the synth.  I use Kontakt5 as a synth, if it makes any difference.  
 

In the X series it is rarely necessary to close views. A better way to manage docked views are the keyboard shortcuts D and SHIFT+D or use ALT+1 and ALT+3 to toggle between track and piano roll views.

Hm.   that's what I'd call a workaround, but thanks.
 

It is a different workflow. There have been a lot of changes since SONAR 5. Learning to work with X series is key to a successful transition.

The minimized synth always settles at the bottom of the screen, so you can just raise the bottom part of Sonar's window to create a space for minimized synths. However, scook is right that there are more efficient workflows, and tradeoffs were made in hte X series to optimize new workflows instead of accommodate old ones. I've gotten into the habit of docking synths so I can click on a tab for instant editing, then use the D and Shift+D commands as he suggests. I don't count keystrokes but if I did, I'd bet I use D more than any other one.