From what I can tell, the built in notein function is monophonic, and only handles "note in" but not "note off" coming in from the keyboard. Is this correct? Is there a way to catch "note off" messages?
Notoff messages also comes in (upon release of a key). You may want to check your setup. The stripnote object it there to actually remove the noteoff messages.
(If so, that would be a way around the polyphonic issue for what I'm trying to do now.) Is there another way to handle a polyphonic keyboard?
MIDI really is monophonic (only one note at a time). If you put a print object at the outlet of notein you will see that all notes do come in. If you want to build a polyphonic instrument in PD you should take a look at the sampler.poly example in the audio example folder. The poly object takes care of polyphony for you.
HTH Soeren