I am assuming you are using the roller writer tip with fountain pen converter. If so, check your barrel hole. One problem could be that there is a little bit of scarf in there, catching the converter or pressing against the cartridge. If its to small or short, it could cause the barrel to catch on the twist portion of the converter, giving it a twist and expelling a slight amount of ink.
I did this once, my barrel hole was almost exactly the length of the converter. It would catch the converter just as it became fully tightened. I used a drill bit by hand, and extended the hole about 1mm. Problem solved.