Attempting repairs can be dangerous....that said !
Are you are replacing a double switch with a double dimmer switch ? If you are then you should have a minimum of three wires at the switch point ,one (live phase)to go to C on one switch, one to go to L1 on switch 1 and one to go to L1 on switch 2. The C on one switch should also be looped to the C on the other . From your discription it looks like the two reds connected together are connecting a live to another lighting circuit.
Stay safe and do not work on a "live" circuit...
john
June 2008