OK I wasn’t able to reproduce that on Safari/mac doing the same thing on a test install, (it did not prompt for a database upgrade again though I didn’t deactivate ACF 4 plugins while updating to 5.0.4 so maybe order of deactivation does not matter). I was doing it before with Chrome/Win7
In any case, when I deactivate ACF 5 Pro and reactivate ACF 4, and then go back to ACF 5 Pro, I get prompted to upgrade the database again, and each time I perform the upgrade I get another copy of the field groups.
Any thoughts appreciated. I’m thinking if I cannot rollback the database I can just delete the new duplicate fields (the ones with higher post ID) since I have not resaved any post/page that uses them.
Thanks. The temporary fix works fine for me for now. The Flexible Content is one instance where I like to change Add Row to something else since these are usually not table rows in my use. Maybe the default can be Add Item in the future. Wonderful add-on.