Grem
Synth GUI open and close for me. I tried changin screen sets, open close the dock. I haven't had a problem with the sythn GUI at all. Granted all I had open was Dim Pro, Z3ta and Rapture.
 
Grum, when you say "as tabs in the Console view on my second monitor" are you saying that you have them in the "Multidock" on the second monitor?
 
Because what I tried above was on a single monitor set up.  

The Multidock had three tabs: Console, Dim Pro, AD2.
I have no idea why I closed the Dim Pro and AD2 tabs but it must have seemed a good idea at the time. I then did whatever I planned on doing next - probably some midi editing - and then clicked on the synth list in the browser to reopen the two synths again.
The screen reacted (like something was happening) but the GUIs never appeared. I checked that they weren't hiding behind the main Sonar screens and then bailed without saving.
The project reopened with the tabs in place and the GUIs in good order.

Grum.

Agreed, intermittent problems are difficult.  I would guess this is why the thread is here and not in the Problem Report forum. There is no project or recipe to demonstrate the problem. At least this forum has many more readers and should it turn out to be a shared experience, a pattern may develop which could lead to a problem report with some specifics. Don't take the move as a slight, there is just not enough information to create a problem report at the moment.
 
 

If it happens once it's hard to say it's intermittent, it would seem more like a glitch of unknown origin.

Anderton
If it happens once it's hard to say it's intermittent, it would seem more like a glitch of unknown origin.

Can't argue with that. I thought I'd better mention it but it isn't making me lose sleep!

Grum