Deleted Groups Still Appear in Find Command

Sometimes there are Groups still in the grasshopper document even after deletion in some Gh definitions. I cannot replicate this problem but I suspect it may be caused by abruptly shutting Rhino down without saving.

Running the Find command reveals these groups, and they are highlighted by the dashed circle as beeing in the top left corner of the canvas.

Any ideas as to what may cause this, and how to programmatically identify and delete them from the document?