Plugin causing homepage to display differently

Had this problem too: in a multisite installation activation of wp-ecommerce on the child sites caused this problem (on primary site not). Startpage showed recents posts, without date, not as an excerpt, without link to the post. Deactivation of wp-ecommerce on child sites solved this problem.
The rss-feed of my sites did not show the feed but even the startpage with the first posts as I wrote. At the moment I don’t know if this were caused by wp-ecommerce or another plugin.