Deleted envelopes

Sometimes when cleaning up (deleting) unused clips in a track, it seems all the automation envelopes beyond that point in that particular track auto-delete.  (Just a dashed flat line through the remainder of the project.)   I'm not certain deleting the clips is the cause, but I later find that the envelopes are gone beyond the point I've edited, that's the only possible cause I can come up with.  Unfortunately I usually discover this later and it's too late to back track.
 
Is there a setting or some method of deleting clips that deletes a track envelope with it?  Or something that's tying my automation envelopes to a clip rather than to the track?  If there's something I can do differently to not delete all my prior work, that'd sure be nice.  (These are track automation envelopes, not clip automation.) 

I suppose that's a possible culprit - but all the automation envelopes from that point forward are deleted, not just a single envelope, and for track (or clip) automation you have to select a particular envelope in the edit filter.
 
In the Track View -> Options -> there's a tick-box for Select Track Envelopes With Clips.  I tried deleting some clips with that checked and unchecked, the envelopes stayed either way.  Not sure what I've done, it doesn't happen all the time and I can't reproduce it on command.