See my original post on this subject. I had exactly the same issue and had to bring the car into the dealer for diagnosis and then a software "Update".
I would call your Volt advisor prior to bringing the car into the dealer since the fix on my 2013 has introduced a few other "buggy" issues that are much more annoying (Navigation Voice commands stopped working, the Clock is now always wrong and the KWH info screen switches between Metric and American Units). From speaking to my Advisor it seems that this is a know issue that GM is working on.
06/04/2012 (1100) Order placed at dealership.
06/05/2012 (2000) Order accepted by GM. Dealer used allocation to place order into production.
06/05/2012 (3000) Order accepted by production control.
06/13/2012 (3300) Order scheduled for production. Order is scheduled into the plant build cycle.
06/28/2012 (3400) Order Broadcast (internal plant paperwork order produced).
08/02/2012 Picked up my loaded 2013 Volt in Chicago