My Custom object instantiated in my XIB file is released… is that normal?

I wrote a NSObject subclass, which I use as a table controller in a dedicated XIB file. This XIB file instantiates this class, which is correctly used until… it is dismissed due to lack of retains!
I did solve the problem simply by retaining it, but I do not see why I have to… Did any of you face the same problem, or did I do something in my code I do not see?