I installed all new devices in a house I'm doing and when I got to the Dining room, I replaced the dimmer switch and got the same results as you guys. Could not figure out what I did wrong. Finally I found out , the switches were never hooked up right in the first place. I just replaced the dimmer with a regular switch and started over. You must locate which switch is the controlling source. I just used the diagram on the switch box. Go buy one 3-way toggle. Once I got everything hooked up right, I installed the dimmer. Caution, I believe you can only install one dimmer on a 3-way set-up. John and Dodgeman, your set-up is just wrong wiring and can be fixed. Ron J.