I've recently bought the LAMY Safari fountain pen (fine nib) with the LAMY Z24 converter. I really enjoy and like the pen, however, I've noticed a problem. When my converter is full of ink, everything seems to be working fine (the ink flow is perfect), however, when it's not full the piston stops the ink flow because of the pressure. In other words, unless I slightly push the piston down, the ink won't flow. Am I supposed to push the piston everytime or is it not properly working?