Has anyone else experienced a brick wall with the FSB for boot/post ?

I'm hitting a wall at 245mhz FSB 1:1 (2Gb Ballistix , M740 , P4C800ed & 1023.001).

Its 100% absolutely error free at 245 in memtest(9hours full tests). But will not even post at 246mhz (regardless of multiplier used).

BUT - I can change the FSB in windows to 250 and its 100% rock solid with all tests ?

Anyone else experienced this.
Im thinking its just a BIOS bug.