I installed Ubuntu 10.10 through Wubi on a Macbook Pro 5,1 late 2008, a dual boot system running Snow Leopard and Windows XP SP3 using refit. I upgraded Ubuntu all the way to 12.04. However when I shutdown I get a series of very quick white flashes after the screen with the little orange dots. When I boot up again refit takes more time to appear than usual, and when I select the Windows icon to get to the Windows/Ubuntu selection screen it stays blank. I have to force a shutdown by holding the power button.

When I boot up after the forced shutdown everything is fine, refit loads up at normal speed and I can access Ubuntu.