United gives bonus miles for doing surveys all the time.

http://www.flyertalk.com/forum/unite...500-miles.html
http://www.flyertalk.com/forum/unite...-delivery.html
http://www.flyertalk.com/forum/unite...ted-email.html

and probably quite a few others.

They probably coded it poorly or used an old template and did not clear both the HTML and the TEXT information, which is why they don't match. It's real easy to do in the mail systems if you forget to regenerate the TEXT and send out two totally different messages without knowing it.

They probably wrote it and just looked at the HTML instead of both when they tested it.

Oh who am I kidding, they probably did not even test it.