Custom type handlers for enums are ignored

I have an enum that is serialized to the DB using a single letter code.
I tried adding a custom type handler for the enum to handle the conversion but dapper seems to ignore the custom type handler.

Given the example code I expected to see the values;
ID = 10, Type = B
ID = 1, Type = Foo

What I actually got was:
ID = 1, Type = 2
DataException, Error parsing column 1 (Type=F - String)

void Main()
{
    SqlMapper.AddTypeHandler(new ItemTypeHandler());
    using (var connection = new SqlConnection("Server=(local); Database=tempdb; Integrated Security=SSPI")) {
        connection.Open();
        connection.Query ("SELECT @ID AS ID, @Type AS Type", new Item {ID = 10, Type = ItemType.Bar}).Dump();
        connection.Query<Item> ("SELECT 1 AS ID, 'F' AS Type").Dump();
    }
}

class ItemTypeHandler : SqlMapper.TypeHandler<ItemType>
{
    public override ItemType Parse(object value)
    {
        var c = ((string) value) [0];
        switch (c) {
            case 'F': return ItemType.Foo;
            case 'B': return ItemType.Bar;
            default: throw new ArgumentOutOfRangeException();
        }
    }

    public override void SetValue(IDbDataParameter p, ItemType value)
    {
        p.DbType = DbType.AnsiStringFixedLength;
        p.Size = 1;

        if (value == ItemType.Foo)
            p.Value = "F";
        else if (value == ItemType.Bar)
            p.Value = "B";
        else
            throw new ArgumentOutOfRangeException();
    }
}

class Item
{
    public long ID { get; set; }
    public ItemType Type { get; set; }
}

enum ItemType
{
    Foo = 1,
    Bar = 2,
}

Reproduce the supplied example around SqlMapper.AddTypeHandler, ItemTypeHandler, and the two Query calls. Trace how the custom handler is selected for enum parameters and result columns, then verify that the queries produce Type = B and Type = Foo without a DataException.