Attribute selection via PCA in Weka

Question

I'm doing an attribute selection using PCA in Weka.
My dataset is KDD Cup 1999, it has 41 attributes (+ label attribute) and close to 25.000 rows.
I use default settings for PCA and Ranker in Select Attributes. I also set the Attribute Selection drop down to "(Nom) Label".
For some reason I get 79 attributes as the result. Could you please tell me why this could be happening and how can I fix this?