LASSO TOOL

as beepster says, the layers can be opened up and comp'ed. overlay (call it what you want) but its really just pieces that need to be bounced.
see sonar looks at over lay as different layers you've made and by default it wont let you just deleted all that content it thinks you want so instead, it just wont let you select it until you bounce it to clips.
 
remember when a clip is in pieces and layered after editing that clip its like scrambled eggs.
you should get in the habit of cleaning up your tracks once in a while (bouncing to clips)
this way you can clean the audio folder and consolidate your projects.
 
your project may be 900MB but your only realistically using 300mb of content.
why not clean it up ?
disk space, it saves a lot of disk space/project space even.
 
 
not a bug at all, its all up to you how you want to work.
sonar is only doing what it thinks you want it to, not deleting material underneath.
keeping the integrity of the layers beneath.