I populate a collection in a UserControl which then creates dynamic LinkButton controls from the collection. When one is clicked, on postback, the collection is empty. Is this behavior by design or is there something I can do to keep the collections populated on postback without re-populating them in code? Do I need to re-query in the forms postback?
Every variable defined in a class inheriting Web.UI.Page will be destroyed at the end of the Page-Lifecycle(incl. controls and fields), hence it will be null at postback if you don't reinitialize it.
One way to persist it across postbacks is to store it in a Session-variable.
You will find a complete list of all options on how to persist variables across postbacks here: http://msdn.microsoft.com/en-us/magazine/cc300437.aspx
It's the nature of HTTP that it is stateless.