bought and installed a 3 way dimmer on our staircase: upstairs still on
its original wall switch, downstairs (at base of stairs) has been
changed from switch to the (correct-type '3 way') dimmer. lite fixture
halfway up staircase.

I was under the impression that the light should still be able to be
turned on from "either end" regardless of what position the other switch
is in, correct? that's how it formerly worked, anyway, with the two wall
switches. but NOW, the upstairs switch must be in the 'on' position in
order for the dimmer to turn on the wall lamp...

wiring all done correctly, near as I can tell, and the only even
remotely possible problem is the fact that our house (3 yrs old now)
originally had the romex 'bare copper' ground NOT hooked to the green
wire on the switch*, where the dimmer now is installed (and the bare
copper ground now hooked to the dimmer green wire)

could the ground "now being used" be causing this strange behavior?

also, if the dimmer is turned OFF, upstairs switch will NOT turn lite
ON. it's a "full sweep knob type dimmer, with the 'push on/push off'
feature at any setting, Lutron, brand new, from a big box store...

*apparently, this 'no ground wire in use' situation is 'correct' for our
home's wiring - I've noticed same situation elsewhere in our house,
inside other wall switch boxes... ?

thanks for educating me, clues and other tips :-)
--
to reply, please remove the "weird stuff" from my email address. thanks.