Do I need to wire it differently then?
Having re-read what you have written in your original post its uncertain how the hallway two way system is geting its power - since you appear to have only connected the three core cables between the upstairs and downstairs switches.
You need to photograph the rear of the upstairs double gang switch with the cables intact. The one you have provided is not clear enough to see how the upstairs/downstairs switches are powered.
If there isn't a borrowed neutral involved the cables should be something like this:
Upstairs switch controlling the upstairs light only: Red (live) = Common and Black (switch live) = L1. This should operate the landing light.
Upstairs switch controlling the hallways light should have three core cable (red = C, blue =L1 and yellow= L2) and the downstairs switch the same - It doesn't matter which terminal each colour goes into AS LONG as they are the same in both switches.
We now have the strappers between the two 2 way switches.
Next you need to get the live and switch live to the switch.
At the down stairs switch you should have a second T&E cable (red/black) which brings the power from the downstairs ceiling rose (light) to the hallway switch.
The red goes in L1 (together with the blue) the black goes in L2 (together with the yellow).
If this arrangement is not in place then we need to see the rear wiring arrangement of the upstairs switch - because it is possible you have a borrowed neutral.
Look at wiki for two way lighting.
http://www.diynot.com/wiki/electrics:lighting:two_way_lighting:lrnonharm[/QUOTE]
I think what the op was explaining was the one way lighting circuit incorporated within the 2 gang upstairs switch. Landing light not part of the 2 way circuit.