"View First Unread" unreliable ?

[Delawaredave5]

Some threads which I'm sure I've already viewed keep starting me at the beginning (ignoring, I think, the "View Unread posts")

Any idea what's happening ?

If you scroll down the first page of a multi-page thread, then at the bottom click to another thread - does that thread count as "viewed" ?

Or do you have to scroll through all the pages of a thread ?

Hope above makes some sense....

Thanks