I used to always mix it till it was pink, but there are two kinds of hardener, cream (oxide red color) and the clear liquid. I used to hang around a body shop and I never saw their filler looking pink, they used Martin Seynour (napa) "cuz" polyester body filler. Since you are supposed to primer bare mettal and As hot as it gets when you mix lots of hardener, I'll bet fresh primer and the heat causes the adhesion problem. Too much hardener makes it too hot to touch...just a thought.
