Backhanded compliments, we've all received some. But, when you're different from society's (or at least the speaker's) perception, there's a formula:
You know, you're pretty for a fat girl.
You are smart, for a disabled person.
You have a good memory, for an old man.
Most of the time, the speaker isn't even aware this is less-than-flattering, especially when it comes to addressing something he/she finds pleasantly surprising. It doesn't occur to this person how it paints his/her misconceptions, how it blunts and boxes the comment.
If I'm a talented for a disabled person, you're telling me my positive (talent) is only good when framed by my "drawback" (disability). It tells me I'm just chopped liver if you compared me to the entire population. Either I'm talented or I'm not. Simple, right?
If I'm average when compared to everyone else, I can handle it. At least your opinion of me would include me as just another person and not one you see as so different it distracts/saddens/disgusts.
Have you ever been "complimented" like that? Have you ever found yourself looking at someone's accomplishments through the lens of his/her disadvantages?