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 the same issue with Xcode 4.3.2, specifically the screen starts going garbled and if you are showing line numbers in your editor those will get messed up to then click somewhere else and *crash*.

Few quick helpful tips I have found:

1. Option-Command-S *before* you Command-Z (Save All) [in case it crashes you don't lose work]
2. If you do undo and you see it's messing up, open up another text file, then click back on the messed up file and it's now all better.

I sure hope Apple fixes this fast!
they fixed this partially in Xcode 4.3.1, it doesn't occur that often anymore