mojoPortal has no control over Bing search results. so your first site has a better ranking for that search than your other site in bing search, that is completely beyond any control by mojoPortal but would have to be based on the bing search algorithm and could be affected by a variety of things like your first site may have been around longer and therefore has a better search rank.

The main thing is to make sure you have good content relevant to the search terms and make sure you submit site maps for all of your sites to both google and bing.

http://www.mojoportal.com/submitting-your-site-maps-to-google-and-bing.aspx

Hope it helps,

Joe