I have a project full of short DI guitar audio clips that I wanted to edit and move around.  All of a sudden, contrary to my three year experience with Sonar nudging a clip left/right or up/down results with the "swallowing" any audio clip that was on the way. Like old Pacman computer game. It does not happen on my other projects and even on this very project sometimes I start Sonar and moving clips goes normally, even though no setting change been made. "Recording Mode" is set to 'sound on sound' but I think 'comping' should not give such a result either. Is this a bug ? or a strangely infected project?

Check Preferences > Customization > Editing "Drag and Drop" section "What to do with existing material:"

This will happen happen in certain scenarios when moving clips around in the Parent track then dropping them over top of existing audio clips. If you drop them where no audio exists then the other clips should remain.
 
Moving your clips with Lanes open will avoid this.
 
If however you are NOT dropping your clip where other audio exists (like just dragging it past another clip is deleting it) then that should not happen.
 
I am on Manchester and tested this a month or so back so if you are on a newer version and this is happenign perhaps it is a new bug.
 
More details would be needed. I may not be back to reply but maybe the others can help define what's up or that alone will help you isolate the issue.
 
Cheers.

BTW... your audio is still there and accessible (if you didn't coompletely cover up the underlying clip). You just need to slip edit the ends to restore the clip(s).
 
Open Lanes to do this.

Also:
 
Check Preferences > Customization > Sharks: Frikin lasers attached to their heads.

scook
Check Preferences > Customization > Editing "Drag and Drop" section "What to do with existing material:"

It has been always set to 'blend old and new' so no - this is neither cause nor solution. And when I say "swallow" I mean that the clips do not get erased. If they happen to lay on the way they stick to the very clip I nudge. To illustrate it better I select clip, nudge it left-right-up-down and it behaves like a vacuum cleaner taking all the clips on the way with itself. Obviously this clips becomes a horrible noise of many overlapping clips. I have never seen this before and my Prefernces settings are same as always been. I doubt you can set Sonar to behave like that, can't imagine what would be the practical purpose ? Of course it makes editing a nightmare.

Beepster
This will happen happen in certain scenarios when moving clips around in the Parent track then dropping them over top of existing audio clips. If you drop them where no audio exists then the other clips should remain.
 
Moving your clips with Lanes open will avoid this.
 
If however you are NOT dropping your clip where other audio exists (like just dragging it past another clip is deleting it) then that should not happen.
 
I am on Manchester and tested this a month or so back so if you are on a newer version and this is happenign perhaps it is a new bug.
 
More details would be needed. I may not be back to reply but maybe the others can help define what's up or that alone will help you isolate the issue.
 
Cheers.

I thought it might be a new bug. Rolled back to Manchester opened a file and it was the same. Rolled up to latest update and first few minutes clips behave normally and then go mad. Infected project? By what,  new update? Then I started new project and clips moving fine (with same settings). Very unpredictable clip behaviour.

scook
Check Preferences > Customization > Editing "Drag and Drop" section "What to do with existing material:"

Let me make clear one issue: I am sure no unselected clip should move when you nudge a selected clip. Please correct me if I'm wrong.

Beepster
BTW... your audio is still there and accessible (if you didn't coompletely cover up the underlying clip). You just need to slip edit the ends to restore the clip(s).
 
Open Lanes to do this.

The audio is still there but and it is accumulated in a selected clip I am moving and erased from the tracks that were on the way. I am sure it must be a bug,  I cannot find and practical use for a such clip behaviour.

When you say "accumulated in a selected clip" do you mean that where two (or more) clips existed, now only one does?  The new clip is a combination of the two? 
 
Sorry if I seem dense, but I'm trying to understand your problem more clearly.