I noticed some UILabels in my iOS projects would disappear when run under iOS 4.3 after I upgraded to the Xcode 4.2 final revision with the GM iOS 5 SDK. I noticed that all the labels that were missing were in italics. Then I saw the reason out of the corner of my eye. Somehow in the Xcode 4.1 to 4.2 project conversion, the font properties on my labels were changed from System. Changing them back to “System” (or specifying the Helvetica family) fixes the invisible label.  Note that in this case, iOS 5.0 did add “Helvetica Light Oblique” as a font choice.

Disappearing UILabel