Question: Anyone have the problem with Undo operation (Cmd + Z) in Xcode?
When I am edit my Objective-C code with Undo operation, some symbols are not correctly edited.
For instance:
was {   

with Undo {{   

XCode 4.2.1

Answer: 
I have XCode 4.3.2 and I have exactly the same problem. This is a serious bug in XCode 4.3.2 especially because of the nonsense edit that it tossed around in various places in the code file that is being edited before XCode 4.3.2 crashes.
Go slowly when using Undo/Redo. I've noticed that it crashes more when I'm hitting Command-Z many times quickly. 

Try turning off the line numbers in Xcode preferences. That seems to have improved things on my Mac. 

Preferences -> "Text Editing" tab -> "Editing" subtab
 uncheck the "Line Numbers" button

From the look of the crash logs, it may be some kind of combination of undoing/redoing (editing) causing the view to scroll or the layout to change dramatically.

From my crash logs:

UNCAUGHT EXCEPTION (NSInternalInconsistencyException): -[DVTLayoutManager \_fillLayoutHoleForCharacterRange:desiredNumberOfLines:isSoft:] *\** attempted layout while textStorage is editing. It is not valid to cause the layoutManager to do layout while the textStorage is editing (ie the textStorage has been sent a beginEditing message without a matching endEditing.)