Puncture/schrader valve/pump question

The front tire on my road bike has a puncture. I have a Schwinn pump
that has two outlets to accomodate regular valves as well as schrader
valves. While the tube is inside the tire, I am able to attach my pump
to the schrader valve on this bike and fill the tube with air (of
course, thanks to the puncture, it promply empties) -- I have no idea
how the pump figures out it's supposed to pump air from the schrader
outlet and not the other one.

To repair the puncture, I took the tire off the rim, and removed the
tube. Now, when I try to pump the tube with air, the pump only pumps
through the wrong outlet (the schrader has been opened to let in air).
Weird.

Any suggestions? Thanks in advance.

-Premal