Given no other information I would blame an off-by-one error iterating over the choices, providing the count of items, maximum index of something, etc.
It might be best to post some code snippets. It looks like you have an array, NSArray, whatever, of strings, and something is going off of the end of it and grabbing some other memory that happens to be... wacky. Is the "Garbage" always the same?
-Lee