Safe to buy food baked in plastic containers:
There are plastic oven bags like this

Source http://lamiacucina.wordpress.com/2014/02/20/saumon-en-papillote-au-citron-vert-lachs-in-folie/
that can be used at temperatures at least up to 200°C. I am sure that there should be equivalent baking pans with similar properties for baking goods.
In conclusion, referring to your link to another question: It depends on whether the plastic is supposed to be baked or not. The questioner of the other thread said he had forgotton to remove a piece of plastic that he had been supposed to. In your case: It is very likely safe.