Warped DBA rotors!!

[The Dok]

About 9 months ago I fitted a pair of DBA rotors (& Bendix Ultimate pads) to the front of the wagon, initially, (apart from the harder pedal I was told to expect from these pads) I was reasonably impressed with the slight increase in braking performance (it is series 1 after all). Over the last few weeks however, I have noticed the rotors starting to warp (pulsating pedal etc), so I removed them, had them machined, & during this process I was chatting to my mate at his workshop & he informed me that it's not uncommon for this to occur, the biggest cause of warping is apparently using a "rattle gun" (of which I'm guilty) to tighten the wheelnuts. He tells me that the (floating) rotors are actually "quite soft" & don't like the extra torque from the gun. I took his advice & shall monitor them over the next year or so, but I must say I was a little surprised by this. Am I the only person who was unaware of this issue with soft rotors??? _