I just made a long list, clicked save, and got a box asking me if I wanted to delete a few duplicate items. I chose yes, then it grayed out and I got a box "Saving..." It hung like that for a long time, and all my work seems now lost.

I tried this on Firefox on the Mac, getting the duplicates popup, but it didn't hang. More likely it was a network problem, or somewhere it hit a limit of how much data could go through a single request. Can you reproduce the issue?

Sorry about the lost data! I need to make that more robust then. I've put it on my list. Safest is to build the list on a separate text file, then past the text directly into the editor, and tweak it from there.