Odd that it'd happen right now when the load is so light.
I'm going to have to play dirty with the db. It sounds like the insertion process isn't working sometimes (probably due to locks and blocking), but not erroring out.
Now that I think about it, I can't 100% swear that when it happened to me, my new post actually "took" and I was redirected to the wrong post as I'd originally thought.
I'm going to be all over this again today. I'm more convinced now that I was chasing the wrong wild goose. Unfortunately, it's so hard to test it because it doesn't happen often enough. It's happened to me exactly once since putting the new db server into production and I'm the one it most needs to happen to since I'm the one who needs to crack the hood open as close to the instant of it happening as possible.