Strange Error in Xcode 4 that persisted across different versions of the same file

I want to preface this question by admitting that I'm still very much a novice, to Xcode 4 and to development in general. But I find I learn the most when I've made mistakes and been able to discover ways to correct my errors.

So I was mucking about in Xcode, following an example in the book I've been studying, in this case trying to determine why the keyboard wouldn't hide when I touched outside a text field. In the process of experimentation, I tried adding an Outlet to the top level View of a View Controller, dragging into the Header file to automagically create it. I knew almost at once this wasn't what I wanted, and I deleted the reference in Interface Builder, and the code it had added to the other files.

And when I did run the program, it threw an exception. Being new to this, I didn't think to check the log files, and when I couldn't work out what the error was, I restored an earlier version of the project from Time Machine, and tried again -- same result. I restored an even earlier version and tried again -- and got the same error!

When I finally did have the good sense to look at the log file, I noticed the reference to the name of the Outlet I had added, but removed! But these were older versions of the code, before I'd even made that change.

I made a thorough search of the code, and my NIB file, looking for any reference to the deleted Outlet. I couldn't find anything.

I eventually replaced the NIB file with a version from the tutorial from the book I was following (it was identical, and easier than rebuilding it from the bottom up), and all was well, everything ran just fine. But now I'm left wondering -- what could I have done to make this error so persistent, across different versions of the file? I'm already kinda uncertain about the way Xc开发者_如何学JAVAode 4 will automagically add code under certain circumstances (that's probably more dangerous than useful for the novice), and I wonder if this is a bug in Xcode 4, or if I inadvertently tripped over a useful feature.

Xcode loves to play tricks on you. I've several times gotten an XIB mysteriously hosed up to the point where I had to delete it and start over. No matter what I'd do to the XIB some elements wouldn't display correctly (or at all).

In a recent case I had an XIB with a label with the text "Start date:". I changed that label text to "Treatment date:", but it still kept coming out "Start date:". I opened the XIB as text and scanned for "Start date:" and it wasn't there. So I tried dragging the label off to one side. Then it displayed the correct words. Dragged the label back to the correct place -- back to "Start date:". I finally deleted the label and recreated it and then the text came out correctly.