Posts aren't appearing as per my preference settings?

[Furball]

My preferences are set so that the first post is at the bottom of the page and you read up all on the same page.

Today - it's not appearing like that, it appears so you read down the page and everything is in pages.

I've re checked my preferences and it is set as I want, so something is wrong somewhere?

To make it more bizarre - some topics are fine, some aren't