Thanks iridiax, you’re absolutely right and unfortunately I worked this one out AFTER I had uninstalled everything!
After I reinstalled everything, I noticed that the problem had moved to my homepage. Then it suddenly occurred to me that I had 10 items default posted to the homepage (and 5 previously) ie it was just some problem in a post. The usual suspects some extra <div> tags. For some reason they didn’t show up in the validation test I did.
I’m kicking myself because I used to have that problem a lot (with embeds) and would never have blamed my wordpress install. I think it’s just because I haven’t had that issue in ages, I just completely forgot.
Oh well, thanks for your help anyway – it’s a lesson for next time! (and maybe to walk away for an hour before uninstalling my blog).
Fortunately the backup looks to be working.
