Unexpected flashdata behavior

[eluser]mddd[/eluser]
Well, $this->data['entry'] is set to the result of get_user($id);
You've said, if you supply an incorrect user id, it does work (in other words: it returns false).
But what are other possible return values. Perhaps if it doesn't find anything you expect it to return false but maybe it returns an empty array or something. That is not 'false' so it would not match your 'if' condition..
So I would suggest checking out what return values you get for different situations, to understand what is happening.