I posted last night about a problem with my feed and questioned whether the problem was with Feedburner or Blogger. Turns out the problem was with a blogger - me.
In Blogger an item is created and titled based on the original title you give it. If you subsequently edit the title you end up creating a brand-new entry rather than overwriting the original item with a new title.
So, I ended up with two identical items last night except for the title. Its kind of counter-intuitive that blogger does this. In most tools the instance of something you're editing doesn't change just because you change the title. Turns out that in blogger they've turned that on its head.
Not sure why it needs to work that way, but it does - and now you've been warned.