UserField - Problem with SPControlMode.Edit

[sarah310]

Hi guys,

I used the UserField-Control in my webpart. If I create a new listitem, the userfield-value gets saved into the SPList. But there's a Problem, when there is a listitem: the control is shown on screen with the right value, but on updating the Control the value gets null (even in the SPList) and after clicking the check-name-button the screenshot appears (picture here

http://picasaweb.google.de/SarahsKopfgewirr/Sharepoint/photo#5070631899507856978)

Create-Code:

UserField bf = new UserField();
bf.ID = bf;
bf.ListId = //is set
bf.FieldName = //is set
if (/*listItem is != null*/)
{  bf.ControlMode = SPControlMode.Edit;
   bf.ItemId = //is set}
else
{ bf.ControlMode = SPControlMode.New;}

Update-Code:

UserField bf = (UserField)editTable.FindControl("bf");
if ((bf != null))
{ listItem[user.Id] = bf.Value;}

Is there anybody out there who knows how to save the Edit-Value?