So What Happened To The Plane?

[Raeven]

But that doesn't explain why the plane was flown -- by pilot and not autopilot -- to an altitude of 45,000 feet, which exceeds this aircraft's "safe" altitude

Why do you conclude that the climb to FL450 was intentional by a pilot rather than an accidentally trimmed climb followed by an override by the autopilot?
I don't know enough about these systems to speculate knowledgeably.

Oh, me, either. I'm completely talking out my ass.

If it was JUST the climb to 45,000 feet, I'd agree... but the additional changes in altitude seem to indicate -- to me, anyway, as I continue to say -- a pilot at the controls, rather than anything autopilot would do.

But of course, reference the first line of my response here and give this speculation the weight to which you consider it due. Min asked for our pet theories; I'm offering mine.