If you "Edit Last Entry", then delete all text, click the "Delete" checkbox, and click "Submit", you get an error: "Posting Failed: No text to post". It shouldn't check for nonempty text if you're deleting.

I also don't see any way to tell iJournal "okay, I don't want to edit the last post, I want to post something new." Closing the window and then selecting "New Post" doesn't do it. Even when I used "Login As" to log out and log back in, the Journal dropdown was grayed out. Only after I posted something in my journal did it ungray and allow me to post to a community.