Symptoms: After a user has changed the system generated view and/or Posts web part. You may see more than one Posts web part. You may also see that clicking the links in the Categories listed along the left hand side of the page no longer produces filtered results, or returns no results where they are expected.

WARNING: Do not try this unless you are completely unafraid of messing everything up and having to move your blog content to a completely new site/list.

Solution:  Determine which of the multiple Posts web parts are behaving correctly. If some web parts have been closed, you may need to do this using SharePoint Designer. Reopen all closed Posts web parts by right clicking and selecting Web Part Properties, then uncheck the Close Web Part box in Appearance section. If any Posts web part behaves correctly, you may safely delete (do not close) the other web parts.  To remove web part customizations, save the page, then right click and Revert to Site Definition. In some situations, if the user has deleted the functional version of Posts web part, this solution may not work.

Recommended Future Action: Designers/users should make a copy of Categories.aspx and work with the copy to determine their changes do not have negative effects before implementing those changes on the system generated pages.