I have two floor pumps - Park model? & a Nashbar pump. Neither grips a presta valve without leaking or occasionally popping off. I used a presta-schrader adapter for a short valve stem in a 30mm rim and noticed that both pump heads work fine with the adapter. Now I use it even when not needed with the short stem valves and no more problems.
I also have a Silca that works great without the adapter, but I broke the gauge on it.