I had the exact problem, so there IS a problem with some of the boards. See my thread
Here 2 Loctite unlocked 800 T-Birds that run at the proper multiplier increments on a KT7, not multiplier overclocking properly on certain Pro2A's. Set it at 900, it runs at 500MHz, set at 950 boots and runs at 600MHz..etc, Read my thread for more info. There are others with the same problem.
There is no official MSI BIOS flash that will fix this problem yet that I am aware of, since I have tried them all. I just sent the board back. It did run well at the default 800, but the board still lacks BIOS options, and my KT7 performed much better when set at 800MHz compared to the Pro2A at 800MHz.