From VS2013 to VS2017 std::async does not start a new thread

I updated my Visual Studio from 2013 to 2017. Compiling was fine but it seems like that the std::async call didn't open a new thread. (I cant see a new one in the thread-window while debugging. Also it looks like the thread which calls the the async function does the job...)

That is my function call:

std::async(std::launch::async, myfunction, this); 

I didn't change anything in my code and in VS2013 was everything working fine.

Any Idea? Google can't tell me a lot about this but maybe i have the wrong keywords. So keywords would also help!

Thank you