Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
27" iMac hints after OSX Maverick Background
Aside from all the hubble-bubble of todays iOS 7 launched, Apple released the new OSX Mavericks background image which is at a resolution of 5120 by 2880.
Think big web designers and developers because this is the massive resolution we saw on the anticipated 27″; retina display for iMac. Along with the discussion of the Mac Pro being able to support 3 4k monitors, Apple are defiantly scaling up the resolution.
Check out some of the latest photos of the Mac Pro here.