Bizarre External Reference Problem

I have a part that claims to have external references even though it clearly does not.  It resists all attempts to resolve the issue.  The problem originally presented itself as a feature with the -> indicator on it, but there was nothing in the feature definition that referenced other geometry.  It was a simple Cut-Extrude with Through All as the end condition.

I have isolated the problem to the sketch that created the feature, even though the sketch does not have the -> indicator on it.  If I delete the sketch, the external reference listed in 'File....Find References' goes away.  Nothing other than deleting the sketch will work. 

I have deleted all relations.

I have deleted all sketch geometry.

I have deleted all features in the model leaving only the sketch.

Nothing short of deleting the sketch works.

The only clue I have to what is going on is that when I delete the sketch (which now has no geometry in it), I see this:

Note the 'Align Group' dependent items.  What the heck is an AlignGroup?

Jim S.