At least for me, I think it (my mistake out of #7 ) was much likely a swampfox problem than a map problem. But who knows; maybe there is some very localized magnetic anomaly right there. It's possible, if unlikely. Maybe I will venture back out there again to see.
Yeah, as I look at the GPS track, it certainly was not a map problem, which leaves the unlikely magnetic anomaly, or the more likely of not looking at the compass close enough.
I did go back out and check (yesterday), and there's nothing weird magnetically there, and the map is fine. I simply goofed up. Not the first time that's happened, and it won't be the last time either.