2gang light switch enigma

[MrsRenovator]

Calling all sparkies,
Ive got a 2gang switch.
One is a 2-way switch (the porch light) which works fine.
The other (the outside light) switches on both the outdoor light.... and the porch light but dimly!
Ah, you say, it's shorting. So I looked inside the switch and found another cable (2core, black+red) ending in the back box. They have both been linked together in a terminal block.
Now here's what I dont understand, the red goes live when the porch is switched on and the black goes live when the outside light is switched on. So it's obvious where the short is, but what's going on? What was the electrician trying to do?
Oh come on, dont go all Health and safety/Part One/ blah blah on me. Lets pretend its academic and you're helping me with a tricky exam question.

 

[ColJack]

he may have put the neutral into the wrong terminal in the light..
meaning that the outside lights neutral goes through the porch lamp to neutral ( splitting the voltage dependant on the laps resistances.. ), hence why the porch light glows dimly..

how exactly are you determining that these wires are "going live" as indicated? neon screwdriver? if yes then throw it away and go and get a proper multimeter.. ( only a tenner... )