Dell Monitor U2211H -- random padlock on screen.

Dell Monitor U2211H -- I have a padlock appearing randomly in the middle of my screen.  I can get it to unlock by holding down the menu button (as many in related forums advised).  HOWEVER, the padlock appears again and again and again.  Is this indicative of a monitor technical problem? Is this something that would be covered by warranty?  It's important to know, because my "limited" warranty runs out on Feb. 24, 2014.