Comment 2 for bug 1694037

The same issue also occurs in MATE. If you right click the mate panel | properties, the mate panel icon appears in docky and stays there even after you close out of the panel properties. With MATE, clicking the icon doesn't affect the MATE panel though.

If I then quit plank and re-open it, and panel icon is gone and it actually does not re-appear even if I go back to the MATE panel properties. However, once I reboot or logout/log back in the issue will return if I go into the MATE panel properties.