IndexOutOfRangeException on Queryable.Single

var form = SqlDB.GetTable<ORMB.Form, CDB>()
    .Where(f => f.FormID == formID)
    .Single();

System.Web.HttpUnhandledException: Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at System.Collections.Generic.List`1.Add(T item)
   at System.Data.Linq.SqlClient.SqlConnectionManager.UseConnection(IConnectionUser user)
   at System.Data.Linq.SqlClient.SqlProvider.Execute(Expression query, QueryInfo queryInfo, IObjectReaderFactory factory, Object[] parentArgs, Object[] userArgs, ICompiledSubQuery[] subQueries, Object lastResult)
   at System.Data.Linq.SqlClient.SqlProvider.ExecuteAll(Expression query, QueryInfo[] queryInfos, IObjectReaderFactory factory, Object[] userArguments, ICompiledSubQuery[] subQueries)
   at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
   at System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression)
   at System.Linq.Queryable.Single[TSource](IQueryable`1 source)
   at GetForm.Page_Load(Object sender, EventArgs e)

public void Add(T item)
{
    if (this._size == this._items.Length)
    {
        this.EnsureCapacity(this._size + 1);
    }
    this._items[this._size++] = item;
    this._version++;
}

T1: Add(x)
T2: Add(y)
T1: Since _size == _items.Length: EnsureCapacity(_size + 1)
T2: Since _size > _items.Length: _items[_size++] = item;
T1: _items[size++] = item <- OutOfRangeException since T2 didn't increase the capacity as needed