Hey PaulSV, the question was answered by the guys.
But, here's what I've experienced. The centerstand picks the rear wheel up, and as you said tilts the bike forward which slightly affects the way the window reads.
I found this out when the bike was new in 01 by filling it to full on the centerstand, then when I rolled it off, it registered above full... Probably not enough to matter, but my worry was getting blowback oil and having to clean it up. So, from that day on I always checked with a warm engine, resting to let all the oil drain for an accurate reading, and both tires on level ground.
Like Red said, just don't fill it all the way to full on the stand and it'll be fine...
Mike :)