Spots & Dimmer

[Daggit]

I changed a one way switch to a dimmer - no probs; but when I changed the lounge pendent to a 4 x 50w spots - the dimmer was killed.

The set up is:

Dimmer - one way - 2 reds only 400w load (250w for GU10 spots)
Ceiling Rose 1 red, 2 blacks, 3 yellow/greens
Existing pendent L, N, E (L connected to Red, N connected to 2 blacks and E connected to the 3 yellow/greens)
New Spots L, N, E

I connected these EXACTLY as the existing connection. When I hit the switch, it popped.

I then re-connected everything again 3 times - nothing. Then replaced the existing pendent - nothing, then replaced the dimmer - it worked.

My question is, could one of the blacks be live, if so, why does it work with the one-way switch? I didn't think that a live and neutral could touch; or could the dimmer have been faulty to begin with (although it worked after I installed it with the pendent), but not with the spots.

I am perplexed by this...

 

[mapj1]

Usually the black from switch to ceiling is the odd one out, and is actually the switched live - try reference section - in this case a picture is worth a thousand words. However, then I'd expect the lamps to be between the two blacks, and the 2 reds to conncet to each other but nothing else. (red+black one is live and neutral from supply to ceiling) Red+black 2 is live from ceieling to switch, and swithced (live when on) returning from switch to live side of lamp.
Could it be this, or a variation on the theme?