The first question: is it leakage of the triac that is the problem, or false firing of the triac? Firstly, SCRs and TRIACs have leakage - its normally specified in the data and can be many mA. False firing is another matter - switching either inductive or capacitive loads means the current phase is +/- 90 degrees to the voltage - this upsets the triac and can cause false firing. Your 40W light bulb fixes this. SCRs normally have superior dV/dT specs so you can wire two scrs "back to back" as in anode to cathode and vice versa. Normally you need a different drive circuit for this to work. This drive circuit is normally two 10R resistors,two 33V zeners and an opto triac like a MOC3052. If you could post your circuit that may help us understand your problem.