Enalkarion

To me it almost sounds like your over heating the joint. My soldering/brazing has all been HVAC related, but when I started out I had trouble soldering. I was overheating the joint and the solder would ball up and run out like you described. Not enough solder or dirt/oxidation would produce the same results. Also when joining dissimilar metals, a solder or braze rod high in silver content was required. Brazing rod is a better gap filler than solder. Just some food for thought.