Ok I found what it was, and it was nothing to do with what I thought... I think I'm actually beginning to get this!
I installed the hack by Bira also which allows posts you've read to be minimised, and because I'd previously installed hacks, I didn't just 'replace' as he asked - but when carefully picking out what he's put in newly, I missed the section on the left side I think, so had a different number of entries as I had places for them to go!
Phew!