Description: A change in the package release 3 caused Plank Dock to not recognize steam. Picture: https://i.imgur.com/6mc6lgo.png
The high resolution icon is what I press to launch steam, but it does not end up under that icon, but a new icon with a lower resolution.

The symptoms are the exact same as when this happened to Google Chrome Beta package in AUR: https://aur.archlinux.org/packages/google-chrome-beta/
Look for the comment "Brottweiler commented on 2016-09-09 12:43".
This was the fix: https://aur.archlinux.org/cgit/aur.git/commit/?h=google-chrome-beta&id=60eff4887a42ac2b15d8c21643fb9758288f2f43

The Steam package doesn't have a StartupWMClass, I am not sure if it ever had one in the .desktop file though.

I believe Plank may rely on information from the .desktop file to determine the windows, so something might have happened to the .desktop file in the 3rd release.

Additional info:
* package version(s): Steam 1.0.0.52-3.


Steps to reproduce:
Update from steam 1.0.0.52-2 to 1.0.0.52-3, then launch steam. Have Plank Dock running to experiance same issue as described.