This could be a Windows issue but I haven't figured it out.  I'm running Sonar Platinum on Windows 8.1.  Some of the older (a year or so) Sonar projects open and I see ALL of the plugins that I popped open.  However, recently I've only been able to see one.  When I open another plugin the last goes away.  In other words I can only view one plugin at a time.  I'd like the way it WAS!  There's probably a simple answer but I don't know it yet.  If anyone can shed some light it would be appreciated.

This has been noticed by others before.  There's a setting for it.  Here's a short example thread where the answer is explained:
 
http://forum.cakewalk.com/Solved-Sonar-Platinum-only-one-vstgui-possible-m3158591.aspx

Thanks lawajava!  I read through it and will check into those recommendations. 

I don't know if it was posted in that thread but there is a pin to sort of pin an open plugin so you can open more and keep that one open. Its to the upper right on the plugin window. Any number of them can be pinned.

Also, holding down the control key whilst opening another plugin achieves the same thing.

yes, the ticket is in Preferences as stated by lawajava.  The slight anomaly is I found that on the very first click to open a new VST GUI it didn't seem to work (the other went away).  However, on the second time everything is back to normal.