When searching for keywords we have in the code (kernel/content/ezcontentfunctioncollection.php):

WHERE ezkeyword.keyword LIKE '$alphabet%'

If you look at items with tag "car" you shouldn't get objects related to
"carnival" i.e. tag results should be strict and without any extension

In order not to break BC, we should add an boolean parameter named "strict_match" (default FALSE) to keyword and keyword_count functions. This parameter should turn the strict matching on and off..