Revit: Moving A Legend on a Sheet Deletes the Legend

I was trying to move a Legend on a Revit sheet a precise distance, so I was using the Move tool rather than dragging it and eyeballing the location. Instead of moving the Legend, Revit deleted it, and issued this warning:

There was no second instance of the same Legend. If there were, why delete all of them? Some on-line searching turned up a case where someone had a Section view deleted from a Sheet when they tried to move it. The offered solution was to look at the Options bar after selecting the Move tool and to uncheck the Disjoin toggle if it were checked. It turns out I did have the Disjoin toggle checked, and unchecking it allowed the Legend to be moved as desired, with no deletion and no warning message. I do not understand why having Disjoin checked caused Revit to think there were multiple instances which then needed to be eradicated, but I am glad that I was able to find a way to do what I wanted to do.