Well, personally "I hope you are the only person experiencing this" :-) But clearly no. The displays control panel... It's wrecked. Not only is the detect-displays button just completely gone ("who needs this?" -Apple Intern) but go ahead once you manage to get the displays working and try to arrange them. Variously the Arrange panel, which I think has been flawless since Mac OS 6 ... Doesn't register your mouse clicks and if it does it may half-draw the screens. I quit and relaunched system preferences several times to no avail to try to make this basic part of the system work again. For years Apple was way ahead of microsoft on display management... and now we're back to the stone age. Thanks for the suggestion on unplugging the monitor. No dice. Randomly I can get it working. It's likely timing related, but the code at this point is completely unstable.