Think it must be an error as indeed it would reduce number of people who pay to upgrade and make it rather confusing what earns TP's and not.

I may try this for a flight next week to see what happens. Don't need TP's right now, so no real problem in very unlikely event they don't post.

But clarification from BA would be great.

thanks

Added: just made booking and right now it does not say anything about additional miles or TP's in the upgrade field, no mention at all. So assume an error and they either fix it now or take it away.