Silverlight DataGrid异常重新排序列标题

I'm trying to set the initial display order of the column headers in a silverlight datagrid by changing the column header DisplayIndex values. If I try to set the column order at page load time, I get an out of range exception. If I set the column order (same routine) at a later time like, in a button click handler, it works. Is this just a bug in the silverlight datagrid control? Suggestions for a possible work around?I'm trying to set the initial display order of