When configuring a key word search, there are settings for "Keyword AND", "Keyword OR", "Start Encapsulator" and "End Encapsulator".
The default setting are:
Keyword AND: ", " (coma space)
Keyword OR: " " (space)
Start Encapsulator: """ (double quote)
End Encapsulator: """ (double quote)
either change the "Keyword OR" setting to something other than a space, or use double quotes in your search.