Yea, the problem's resolved. It was related to the recent glitches with the new server whose time was off by 6 hours.
What happened was that I made a post via the old server. Then I somehow ended up on the new server (maybe because that's when the new server was brought online, or because the load balancer decided that I was better suited for the new server).
Since the new server was behind the old server by 6 hours, it looked at my posting history and thought, "he last posted negative 6 hours ago! that's less than 15 seconds ago".
The code65537 account was unaffected because, as a new account, both of its posts were made on the new server, so there wasn't an unusual 6-hour discrepancy tripping up the cooldown timer. And my main account worked fine if I logged in from a different geographical location (so that your load balancer put me on a different, unaffected server).
But now that it looks like the server times are properly in sync, there is no issue.