Sometimes when I've got four or five envelopes on a track (controlling volume, and three or four plug-in parameters) suddenly I'll go to move a segment between two nodes and it snaps right back into place.  It freezes so that all of the envelopes are stuck exactly how they're drawn in.  Even if I delete them, save, close the file, re-open, re-create the envelope, still it won't budge.  Why is this happening?  
 
I use Sonar 8.0 by the way.  
 

(covering up my mistake by deleting it).

It's a bug. You have to close the project and re-open it to get back the ability to move automation nodes. I forget now what action gets you into that weird mode, but it has something to do with double-right-clicks or holding down the control key while clicking on an envelope during playback, or something like that.  I know it had to do with inserting nodes during playback, and when it happened I'd just save the project, close and re-open it. It was fixed in 8.5.