Ehmer, 21, has made 14 appearances for the Cumbrians since joining them in early November, making his debut in the 2-2 home draw against Wolves.
"We're obviously disappointed because Max has been fantastic for us," manager Graham Kavanagh told the club's official website.
"He's shown us that he has real quality and has been a big part of our squad since joining us in November.
"QPR have been really good with us and we completely understand this kind of situation. We wish him all the best as he heads back down there."