Mixing down 3 tracks, each track has pro channel eq, compression, and rematrix verb.  Automation lanes on volume sliders.  Each track has the following FX: Para-EQ, LP64-EQ, and stereo imaging.  One more stereo imager on master out.  During playback the master mix peaks at -6.  During mixdown solid clipping, bright orange and red, through the roof...been fiddling for days and I can't figure this out, it's never happened before.
 
Is this a bug?  Playback sounds good but exports and bounces are useless so I have a mix stuck inside of Sonar, now what?
 

No it's not a bug otherwise there would be hundreds if not thousands of complaints!
 
Describe how you've set your routing up.
 
Does EVERY track have its OUTPUT routed to a bus? (In other words NOT directly to your main out/Interface)
And does every bus have its OUTPUT routed to the Master Bus (The one that YOU have to create and route directly to your mains?
 
If you mute your Master Bus you should hear total silence. If you don't, there's a routing problem

Thats interesting.
 
Maybe take a couple of screenshots and put them up?
 

Are they mono or stereo tracks, and is the master bus set to mono or stereo?

It has nothing to do with routing.  One mono track, two stereo tracks, out to a stereo bus then to main out.  So much lost time in this mix now.  Been using cakewalk products since 2001, never had this issue before.

Without screen shots, it will be very difficult to figure out what's anomalous. Meanwhile until you figure it out, Select All and bounce to a new track, making sure of course that the master level doesn't hit zero. Then you can drag that track out to the desktop (or wherever) and have your mix.

What kind of mix down? Obviously not fast bounce export?
What's your hardware output bus look like?