Err: cursor (caret) not displayed in text box but it allows to type characters ...

While :   Working with focus event of an HTML element
Reason:
     Text box holds its last locked stage still.

Solution:
           That text box item should be updated to current setting. For that call obj.UpdateLayout() before call focus().

  
Ref : http://forums.silverlight.net/forums/p/23888/370525.aspx