Note that the Viewer/VFS Plugins category is for posting viewer plugins and VFS plugins.
Questions about the viewer etc. should go to Help & Support. Please use the right area, else your post gets put into the moderation queue and we have to move and approve it.
Regarding the icon, you're probably confused by the way the Windows 7/8/10 taskbar works. If taskbar grouping (or "Hide Labels" as it seems to be called in the Taskbar settings UI) is on, which is the default, then the icon represents the application, not any individual window. You only see individual window icons when you hover over the application icon.
If you turn off grouping on the taskbar, you'll see a different icon for viewer windows compared to other windows.
(You seem to have two Opus application icons on your taskbar, and I'm guessing that if you unpin both and then re-pin whichever remains, you'll then only have one.)
You can also install this add-in to separate viewer windows into their own group on the taskbar, which will also make the viewer icon appear at the top level of the taskbar, distinct from the Opus application icon: