That's the point, in those circumstances I'd have shot Manual too.

I'm not some kind of AV Fascist.
BUT, remember this is Talk Basic, and we're seeing an awful lot of people who are being coerced into shooting Manual without any understanding of Why.
In your situation last week, they may not have realised what was happening with the reflectivity of the scene shot to shot, and may well have adjusted their settings. They're shooting Manual - so it must be right?

But they end up with horribly inconsistent results.
You can hear their questions now, or they wouldn't even bother coming back to ask - because they'd been told to shoot Manual, they'd got rubbish results - so it must be their fault :shake:- or maybe there's a problem with their gear? Perhaps they need to buy a 5d to improve their photography, but not a Mk1 because there aren't enough MP's, and not the Mk2 because of the horrible banding issues. And all of this based on the truth - as provided right here on TP!:nuts:
Which is why I keep saying - it's not the exposure mode that's important - it's understanding your meter.