Are my strobes working?

[Dubious Drewski]

Hey all. I just bought the Opus M1002 lighting kit. I've got the m100SR strobes set up and working as slaves, but there's something strange going on. I press my shutter, my camera's onboard flash goes off (It's a K10D), and the strobes fire. I can clearly see it all happening properly. BUT no light from my strobes is getting into the photograph (only that tiny bit of my camera's onbard light). The strobe's timing is off, obviously. Through playing around, I found out how to make it work. I set my shutter to trip after a 2-second delay. This causes my camera to emit a preflash, and this somehow makes the strobes fire on time and show up nicely in the photos. It doesn't work with the 12-second delay or no-delay, only 2-second.

Is this normal? Is this how I have to do it?

(This kit came with zero instructions, which I think is a terrible, inexcusable thing)