This is due to the double matching problem: for example, pair "Tehran Times (Tehran)"/"Inter Press Service" (from INT) is scored more than 1.0 because "Tehran" matches "Inter" twice: even with a low score as a coefficient, "Inter" has a high IDF compared to "Press" and "Service", so counting it twice makes normalization wrong.
this problem may be solved by choosing a more adequate sub-measure: experiments show that using the CosTFIDF measure with bigrams or trigrams outperforms standard CosT-FIDF.