Are you selecting the Experiment only option?

I do have one other question: Have you gotten any other changes like stats or gender or filling your pet up? Because I spoke with a programmer and it could be one of two things.

1. Your browser is storing in its cache the first experiment result that you got. Try clearing your cache and see if that gets a different result.
2. If you get stats and other stuff then that means that it is just bad luck that you haven't gotten any other change.