Sketch considered "Used" by Used sketch Tree Filter despite no longer being used by a feature
I am using Creo Parametric Release 7.0 and Datecode7.0.6.0
A sketch is considered used even after the feature that used it is deleted.
I like to disable the Used Sketch option in Tree Filters because I don't like cluttering my tree with unnecessary sketches. If I use a Sketch 1 in an Extrude 1, Sketch 1 appears nested under Extrude 1 and Sketch 1 no longer appears at the top level of the tree. If I then delete Extrude 1, Sketch 1 does not reappear. Not until I re-enable the Used sketch option in Tree Filters.
This does not make sense because Sketch 1 is no longer being used. Why does this happen? What is the purpose of a Used sketch filter if sketches which are no longer used don't show up again? How do I delete a feature and leave the sketch "unused"?

