I'm not at all an expert on this hot topic but while reading about this Twitter flare up it reminded me of a piece Kaskade wrote about the politics of Mash-ups which I found appropriate:
"The politicking of a mash up is nothing new. Hip Hop has been having
this conversation since its inception. Sampling other people’s work
comes with a price. And it makes sense on one hand - why wouldn’t you
compensate someone who created something you’re using? A writer can’t
just plagiarize another writer and call it inspiration. An artist can’t
cut and paste other artwork and claim it as their own. Why would the
rules in music be any different? Calling it a mash up, a tribute, a
homage or a remix: does it even matter?
I can tell you that it does. But the devil is in the details, and comes down to intent.
.....When I bring them [Mash-ups] out, I’m certainly not claiming that they are my brainchild alone and in fact always always give credit to every artist involved." (Source: Kaskade's Tumblr)
Maybe Headhunterz polite request is the most apt response of them all: