Two 15 amp circuits joined

I have a odd situation with my christmas lights. I have two intermatic timers in the garage each with its own 15 amp breaker. One controls the plug which the cristmas lights are pluged into, no problems with this circuit. The second timer has another plug outside under a blue spruce to light it up with christmas lights as well. What I found out is that this timer is also conected to the front porch light which is on third circuit. When the front porch light is on, power is fed to the timers circuit even when its open (not on). It all works fine, until the timer is off and all the lights are on, i.e. christmas lights on the tree and the lights on the third circuit. Everything works ok when the timer is on. I was wondering if this wiring design is to code?