Search Keywords not working if added to any other site collection other than Search Center sitecollection

I have so many different site collections and one of these site collections hosts SearchCenter site as well. I wanted to use the same search center 开发者_开发问答for all the site collection in SharePoint so I changed the search settings of each sitecollection to point it to SearchCenter site. Then I added Search Keywords in each site collection for various things. What I have noticed that I am able to search only those keywords which are defined in Search Center site collection. All the other keywords doesn't display any records in BestBets webpart. I can see the results in the Bestbets webpart only if I search for the keyword which is defined in SearchCenter site collection. Is this behavior by design? If Yes then what is the purpose of having this feature available to each site collection?

Keywords and best bets are site collection scoped, this is by design.

For more on why and SharePoint IA in general see:

http://www.kmworld.com/Articles/Editorial/Feature/SharePoint-the-backbone-of-your-information-architecture-53955.aspx