It would appear we have the double post bug surrounded. It's 10 minutes past its normal arrival time, and no double post to be found.
There's been a slight change in plans, however. Rather than re-enable each plugin now, I'm going to leave the plugins disabled overnight, and check on it tomorrow.
If the bug is still gone, then we can be certain it's one of them. If I start in on it now, and the bug kicks on and it doesn't work out well, we won't know for sure it wasn't just late.
This way we'll know. And diagnosis will be a matter of from there, and not long at that.