To all Blogger users:
Right now, all posts that are saved as drafts are automatically being set to not allow comments if they are closed first and then published later.
In other words, if you create a new post and then publish it right away without closing that post (even if it has been saved over and over), comments will remain open. If you create a post and then close it, when you open it again, you will find under Post Options that your comments have been set to "Don't allow; hide existing". The auto-save feature doesn't seem to be the problem, it is in closing and re-opening that things go wonky!
Once you set the comments to "Allow" they will stay open unless you close the post without publishing and then re-open it later. They are aware of the problem, but I have started checking my Post Options before publishing just to be on the safe side.