But there shouldn't be any extra shear force on the bolts (ie below the head, as Mr Bomb pointed out), as the friction between the spacer / hub / disc should prevent any movement...
It's a Rolf Dolomite on a 2000 Marzocchi fork, with a Magura Julie (2003ish IIRC - big rotor already!)... I've used the fork with a different wheel before, so despite the lack of 'proper' investigation, I'm pretty certain it's the wheel that's at fault! I've found one reference to a difference in the iso standard, but nothing definitive... :?