RecentDocumentManager listed items grayed

I sure I'm just missing something - I use Deserailize to get recnet items in the RecentDocumentManager

for example

using (StreamReader streamReader = new StreamReader(recentFilestr))
{
string line ;

while ((line = streamReader.ReadLine()) != null)
{
sb.Append(line);
}

}
recentDocManager.Deserialize(sb.ToString());

and I get the expected items of the recentlist I saved but the items are all grayed out and un selectable.
Can anybody explain why