Why is Dictionary.Add overwriting all items in my dictionary?

Question

I have a dictionary of type Dictionary<string, IEnumerable<string>> and a list of string values. For some reason, every time I do an Add, every value in the dictionary is overwritten. I'm completely stumped as to why this is happening. I made sure it's not a reference problem be declaring and initializing the IEnumberable object within the loop so that it's scope does not go outside one iteration, and it still does it. Here is my code:

foreach (string type in typelist)
{
    IEnumerable<string> lst = 
        from row in root.Descendants()
        where row.Attribute("serial").Value.Substring(0, 3).Equals(type)
        select row.Attribute("serial").Value.Substring(3).ToLower();

    serialLists.Add(type, lst);
}

where typelist is an IEnumerable<string>, root is an XElement, and serialLists is my Dictionary.

Answer 1

This is a captured iterator problem.

Try:

foreach (string tmp in typelist)
{
   string type = tmp;

(and the rest unchanged)

Alternatively, I would evaluate the expression during the add, I.e. do a .ToList() in the .Add:

    serialLists.Add(type, lst.ToList());

The second option is probably more effective overall, although it does force evaluation of thigs that might otherwise never be needed.