I wonder if it's a pre-load/surge prevention measure done by the PSU.
Now I will have to research it further.
I think you're right. I don't have this PSU, but thinking about it, it sounds like the PSU might have some kind of protective feature where it turns on on partial voltage, checks for problems, then switches to full voltage. This would be a good thing as PSUs are most likely to fail during power on due to the large starting surges. Your motherboard does get a pretty good kick when it comes on(there's been discussion on how bad this really is) but this could be a way to try to reduce the starting surges thereby prolonging the life of the PSU and the components.