B767 Captain reported unexpected flap and speed warning messages during cruise along with an uncommanded thrust reduction by the autopilot. The flight crew disconnected the auto throttle; contacted maintenance; and monitored the aircraft systems until reaching the destination airport.

Narrative

After departing ZZZ and in level flight on ZZZ1 prior to the ETP (Equal Time Point); I happened to be looking at the Attitude Indicator when suddenly the Fast/Slow scale and indicator became amber and started flashing. The diamond was pegged on 'F'. The speed bug remained on the commanded cruise speed .of 80 Mach and never moved. 'Flap Limit' was displayed in amber on the Attitude Indicator. The flap indicator showed the flaps retracted in their the commanded position and the flap handle was fully in the up detent. The auto throttle subsequently began reducing the power smoothly to idle. As I had been watching this unfold and noticed the thrust reduction; I instructed the Pilot Flying (PF) to address the power state. He immediately manually stopped the throttles before they reached idle. The Throttles were then manually pushed up; but the autothrottles resisted and the PF disconnected it. Even with immediately recognizing this insidious; silent event that if unnoticed could lead to a high altitude aircraft stall over the featureless ocean on a moonless night; 10-15 knots were lost and the subsequently recovered. We contacted Maintenance and our Dispatcher on a satellite call. A subsequent sat call included the duty pilot and an Engineer to determine what was occurring and whether a return to ZZZ was needed. After discussing this as a team; the First Officer and I decided to continue as long as the event did not reoccur or there were no other system or electrical anomaly's that surfaced. None of us had experienced this before. It appeared to me that the event initiated with the aircraft systems determining the flaps were out of up at cruise followed by the autothrottles reducing power below the command bug speed to protect the flaps. Being that there is no aural caution associated with this failure/anomaly; I'd like to know more about what was determined by maintenance after they addressed the issue