3-Way wired odd?

Not that I have seen everything, but I have not been able to find this
3-Way wired this way in any of the books I have. This 3-Way switch is
being replaced, which is my interest in this.
Background:
Keep in mind, I didn't set any of this up. This is how it has been
working. There is a hallway to the garage from the family room. There
is a 3-Way switch on the side of the door to the family room to
control a light in the hallway. At the other end is a motion detector
switch which has the switch position of on/off/autio. It is left in
auto almost all the time. When you come in from the garage or upstairs
from the basement, this hallway light comes on. Likewise, if you come
from the family room and open the door, the light comes on. If you
want the light in the hallway on before you open the door, you can
click this normal 3-Way switch and it turns the light on in the
hallway. After no motion, the light turns itself off.
I took the cover off for the 3-Way switch and it doesn't look like
anything in the books I got. It has a black wire side wired to the
copper screw connection. A white wire side wired to the brass screw. A
red wire side wired to the brass screw. (This is the part I don't
understand.) The brass screw from the red wire has a YELLOW WIRE
JUMPERED TO THE COPPER SCREW THAT HAS THE BLACK WIRE SIDE WIRED.
(Sorry for the caps, but I don't think you can bold text in a
posting.)
Why is there a yellow wired jumpered between the brass and copper
screws?
Does this allow the switch to be toggled to turn the light on, so that
the motion detector on the other switch can shut it off itself?
Should it be wired this way?
I'm replacing the 3-Way there with a new one, should I just wire the
replacement 3-Way switch the same way?
I admit I don't often have a need to put the light on before I open
the door from the family room, since the motion detector works fine
for this, but I don't feel like I should just remove this 3-Way
switch. Some people out of habit would just except it there to have
something to click before going in the hall way if they wish.
Please be kind in your reply. I do have a call out to a pro for things
I can't handle. I've been successful in replacing other switches and
outlets in the home, and with the help of this newsgroup I have
certainly gained a better understanding of things. Thanks!