An old post, but I thought it worthy to reply.
All I can say is that I have had never ending problems with the Planet Bike floor pump that I own. I have had it for a few years and share the use of it with my partner. I use the schrader hole, my partner uses the presta hole. The head unit internal rubber wears quickly and loose bits of rubber form. I purchased my pump at a local bike store and they have kindly replaced the head a few times for me. The problem seems to be the internal valve in the head. It requires back pressure from the tube. My experience has been that if the tube is flat, then the valve does not switch over at all, or very well. It seems to be a design flaw, and more annoying for me, is that it seems to 'stick' on the presta side, meaning I can't pump my schrader tubes if they are flat.
I have had to resort to pumping the schrader tube with a small hand pump to build a bit of internal pressure, then transfer it to the Planet Bike Floor Pump. I have found that sometimes this new pressure helps the valve to switch over in the head, sometimes not. I am planning to either throw out my planet bike pump, or put a proper head on it that can be interchanged to either a single schrader head OR a presta head, not both. I think the designers of the dual head have tried to achieve too much with it, and did not seem to test out its limitations. The dual head is a bit flawed in my view and experience.