Negative keywords appear at the bottom of the keywors list (marked up in the brown colour). A very likely cause for not getting negative keywords is the default setting of "max. wanted", which is 500, meaning that only the top 500 keywords are given. To get negative keywords, adjust the setting by defining a very large number (e.g. 99999) for this parameter.
BTW - a Key keyword list never includes negative kwywords.