I seem to be experiencing a completely different issue now. The 2.8.1 upgrade fixed the crashes on dragging/dropping issue for me, and I was very excited. However, something worse seems to be happening now. Taking a new screenshot seems to overwrite the previously saved screenshot. To reproduce:
take a screenshot with skitch
set the filename at bottom left in skitch, i.e. "test1"
drag/drop it into a folder in finder
take a second screenshot in skitch
note that "test1.png" (the saved version of the original screenshot) vanishes as soon as you take the second screenshot.
I'm on Skitch 2.8.1,
OSX High Sierra 10.13.3