It happened today on the Monster too.  Last week the rear tire on the Motard slipped pretty good on a right hand turn at about 50mph on a dry overcast afternoon.  The tire then caught and I straighted up mid-turn, slowed, and went straight to a stop off the road.  The tire looked OK and I figured it had some mud on it from the prevous day.
Then it happen slightly again later.  I do not push it very hard or deep while cornering so I'm not sure what is up.  Pressure and tread look good.
Then today on the Monster it slipped (same situations) but I slowed and finished the curve.  Tire looks good as well.  This is new to me.  Tires are both one and two years old respectively, and this is not new to me.  Am I missing something?  What should I check?

what type of tire and were there tar snakes covering the cracks? 

If you had been riding for a while, your tire should have been warm enough not to slide on you, even as cool as it has been. Maybe the rear tire could be starting to dry out and get hard. Even if you bought it only a year or two ago, it could be much older.
A lot of dealers have old inventory, due in part I guess to the crap economy and riders trying to stretch a buck.

I change the rubber on my bikes every two years regardless of wear. And the last couple of times I have been sure to look at the manufacture date. If it's over a year old, I won't accept them.

Thanks John, I'll look for the date.

I'll put new tires on for you if you decide to go that route.

Thanks for the offer.     Who knows, I may end up taking you up on that.