Still not quite sure why you got this. Couldn't replicate. I'll be checking error logs, etc to ensure whatever it was doesn't happen again. Only receive 3 404's for something like 2k visitors yesterday.
Did you change the post title? I figured since your URLs contain the title then that's what must have happened. Works now though :)
Sort of... I had the post open in two tabs, one tab with the original title, one with the title I posted here. A few seconds after posting I noticed a sentence I didn't like, tweaked it in the wrong window, hit save, saw the title change, switched it back. You must have hit in that few second time frame.