Hi, I just hooked up my MBP 2010 to an additional LCD display using Apple's MiniDisplay to DVI converter. Then I changed preferences to use the additional display as my primary display because it's bigger. I noticed 2 strange things with this setup on Mountain Lion and I'm wondering if anyone experienced something like that: 1) When I was opening the System Preferences window right after switching the primary display settings, it was still showing up on MBPro's display and not on the additional display currently set as the primary display. But after dragging it on the primary window, now it works the way it should (it opens on the primary display). 2) Opening applications, when using additional display set as the primary display, changes the behaviour of the Dock: the dock starts to hide and show automatically. However option "Automatically hide and show the Dock" in the System Preferences is unchecked. If I check it and immediately uncheck it again, the Dock stays on - the way I have it set up - until I launch another application, that is. I think the 2) could be a bug in Mountain Lion.