Does a typical floor pump have an integrated one-way valve?
There is a valve in the floor pump, yes, so it is supposed to press in the presta valve the whole time it is attached to it.

I too have seen the problem you refer to in the comment on @Useless's answer - diagnosis has always shown this to be down to the presta valve either catching on the side of the pump fitting or just being stiff and refusing to budge.

A simple solution I use is to give it a quick press with my finger before using the pump, just to ensure it moves cleanly and isn't stuck.