I'll keep trying things. But I think you may be right. When this problem first showed up I thought it'd be about a 50/50 chance that it was a hardware problem.
I ran the latest upgrade last night, Hoping that that would fix it, but no.
The workaround is obvious and easy.
If I find the solution, I'll post ti here.
The fix may involve a new N810 for Christmas.
Thanks to all for trying.
Alan