My take on it was that they thought people would be too busy to notice that they had an earnings warning and the downside would be minimized. Most people probably already did all of their tax loss selling in the last couple weeks.
They had to give a guidance warning now which means that the really worst case is now discounted. Smart shorts covered today and smart longs bought. The shorts we see on this MB are just paid bashers w/o any families to spend Christmas with.