I've just removed and reinstalled WordPress from a clean download, and this is still happening.
Here are two things I should mention in case it helps:
- Both times, unzipping the downloaded folder resulted in a number of duplicated files: for example I ended up with five index.php files. Originally, I kept all of them on upload under different names. On the reinstall I overwrote the duplicates.
- When I first installed WordPress, after logging in I was taken to a blank page. I followed the instructions here:
...and solved the problem. I did the same again on the reinstall.
Could either of these have affected the dashboard issue?
EDIT: And something's clearly gone wrong with the reinstall as the site isn't loading anymore. I'll have to look into that.