Thanks for bringing this bug to my attention! I was not aware of it, mainly because - you may be in for a surprise - Duolingo has finally implemented a native drag-n-drop feature.

It was still under A/B testing until recently, so I didn't know what to do with the extension, but now that it seems to have finally made it to all users, I'm going to release a new version that only supports the keyboard shortcuts feature (that should fix the bug in the same time).