A319 CREW ENCOUNTERS MOUNTAIN WAVE; WHICH CAUSES ACFT TO CLIMB 600 FEET AND EXCEED VMO BY 10 KTS.

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AT FL390; IN SMOOTH AIR; CRUISING AT .79 MACH; WE GOT INTO A MOUNTAIN WAVE AND THE AIRSPD INCREASED 20 KTS WITHIN JUST A FEW SECONDS. THE AIRSPD INCREASED INTO THE BARBER POLE BY 10 KTS. AT THIS POINT; THE ACFT'S OVERSPD PROTECTION FEATURE TOOK OVER AND STARTED CLBING THE ACFT. I HAD SELECTED A SLOWER SPD AND PUT THE SPD BRAKES OUT TO SLOW THE ACFT. THERE IS NO WAY TO OVERRIDE THIS OVERSPD PROTECTION. WE WENT UP TO FL396 BEFORE I REGAINED CTL OF THE ACFT. WE DSNDED BACK DOWN TO FL390 AND RPTED THE CHANGE OF ALT AND MOUNTAIN WAVE TO ATC. I DON'T SEE HOW WE COULD HAVE DONE ANYTHING DIFFERENTLY OR CHANGED ANYTHING TO IMPROVE THE SITUATION. SUPPLEMENTAL INFO FROM ACN 733052: STRONG MOUNTAIN WAVE ENCOUNTERED AT FL390; ACFT'S MAX CERTIFICATED CEILING WAS EXCEEDED BY 600 FT AND VMO EXCEEDED BY 10 KTS. (AIRBUS ACFT AUTOMATICALLY PROTECT THEMSELVES BY PITCHING UP IN OVERSPD SITUATIONS.) THE MOUNTAIN WAVE CAUSES THE AIRSPD EXCEEDANCE AND THE BUILT-IN PROTECTIVE FEATURES OF AIRBUS'S AUTOMATION CAUSED THE ALT EXCEEDANCE.