weird voltage requirements for OCing

[SammyBoy]

I just put together my Tbird 900 System, and I to boot it at 1.75V, no go, try 1.85 no go, the damn thing doesnt want to boot at anything above its stock 900 with any voltage I throw at it,

so i take off user control, let it do whatever it feels like doing, and voila!
1.05 gigs, 1.1 gigs, 7x143fsb, it does whatever the hell I want,

pretty weird...but cool