Footnote duplicates when dragged and dropped

I’m seeing some strange behaviour with footnotes. It’s not consistent in all documents or present in all projects, though I can reproduce it in one particular document.

It’s simple enough. I use inspector footnotes, and frequently drag a footnote from the inspector to a word in the editor in order to change the anchor point of the footnote. Usually this just moves the footnote – in some instances however it duplicates the footnote, leaving the original footnote anchored in its original position, and producing an identical footnote anchored to the word to which I dragged the original. As I say it’s a strange one, not consistent. Has anyone else seen this behaviour?

Perhaps this should be posted in bug hunt. If so please move.