You remember how FA introduced a nuke button to save everyone a mouse click when clearing their submissions box (which they do a lot, because we know how conscientious people on FA are about their database footprint)? It's apparently not the best-coded functionality in the world.
I have a phantom notification - it says there's one submission notification, but when I go to the submission notifications page there's none. (If I get more, I see those, plus the phantom one.)
There is a known issue with the message counter getting out of sync when nuking messages.
If the next time you get a new message of that type in your message center, you check the box under it and use "remove checked", it should force the system to re-count and get you back in sync.
Please let me know if this works out for you.
I fully expect it not to work because of how bozotic this sounds, but anything is worth a try once. e: It worked, but it's still bozotic.