Bouncing Clips Sometimes Hang

So far X1b has solved nearly all my woes, but one thing it hasn't solved is that Sonar periodically will hang when I go bounce clips together.  The status bar (in the Control Bar) will appear to be working, but it will seem like it's going to take a year to process.  The "x" to cancel the operation is not visable, and the only way I can cancel it is to force close Sonar.  Has anyone else run across this, and any idea why it happens?  It is random enough in my world that I can't create a recipe that makes it happen every time.
 
thanks.