[CentOS] Question about centos 4 or 5 install with software RAID

When doing software RAID-1 installs on reboot (just after install)
I ALWAYS get RAID device is not clear - preforming reconstruction.

Why is this? If I just installed the array should be in sync shouldnt it?
And clean?

Not that this is a big deal - it just seems odd. It does reconstruction and
life goes on.

Is something special at install time that we are only installing on one disk
of the array and after reboot it now says we are unclean and populates the
second disk in the array?

Thanks,

Jerry