I have a Workspace saved (actually, it's a four-workspace session) that has both .acc and .acc.accord extensions. But I don't recall creating two--I've only just created and saved the one session, and then save it (replacing the old version) whenever I update it.
This is most recent Accordance on most recent OSX on a 2008 iMac.
Anyone else having an issue here? Which is the one to keep, or does it matter? Sorry if this has been discussed before on the forums--I don't have time to look into this at great length just now.