Dirty console switches can cause intermittent operation like this one. Anyone spill coffee lately?
Try some electrical contact spray (Radio Shack has some) on the switch terminals...90% of the electrical problems experienced are caused by dirty or corroded terminals.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car