I've been seeing this problem since around last Thursday. The problem occurs when an app you have installed shows up in the search results. If that happens, then the arrows will be grayed out and it won't be possible to go to the next page of results. Also if more than one app you have installed shows up in the search results, only the first app will show as installed.
There used to be more problems such as the app store not allowing you to review apps you've purchased and never showing any installed apps as such, but those appear to have been fixed. Searching is still a problem though.