It may be an intermittent fault, software/server? I just done a couple of tests with the option of 5 posts per page and it appeared fine.
As a rule I have my option set at 30 posts per page, the default setting is 15.
You can change this option to what ever you like by going into your user cp and select Edit Options --> “Number of Posts to show Per Page” it’s a long shot but you never know, maybe something is tripping up on a certain value worth a try for the time being.
