This works fine for me on Windows 10 1511 64-bit. I don't think it is a bug in an Adobe product as much as something not set right on your computer.
What app is the default opening for PNG files, now?
What actual name is listed for Photoshop in the Choose Another App list? If it's Adobe Photoshop CC then it's a few years old and should also include 2015.5.
This is what I see when I Choose Another App for a PNG and clicking on the PS then Ok opens PS: