Re: bbPress cannot count properly after upgrading
Did you try recounting from the admin panel?
Admin > Site Management > Recount
"The following checkboxes allow you to recalculate various numbers stored in the database. These numbers are used for things like counting the number of pages worth of posts a particular topic has. You shouldn't need to do do any of this unless you're upgrading from one version to another or are seeing pagination oddities."
(sure wish blockquotes were styled here!)