I'm not sure how that goes... I can imagine people download a house, adjust it and someone says: "Wow, that looks great what you did to it, can you upload it for me to the gallery?!" I'm not sure if you can see who the original creator is..? Because if not, I can imagine you won't remember. If you can then yes, it would be the decent thing to do to add that information to the upload. But I kind of can imagine people forget that in the process of playing and building and adjusting and sharing. I don't think it's always meant as stealing.
