If I open an epub in the editor via the file manager Open With I get an editor icon in taskbar, if I then open an epub in the viewer via the file manager Open With I get a separate editor icon in taskbar - i.e. standard windows behaviour.
However, when I open two epubs from calibre, one with the viewer and the other with the editor, the taskbar icons for the viewer and editor are grouped! Grouping taskbar icons is a standard feature of Windows 7 (right click taskbar, Properties, set Taskbar buttons: to Always combine, hide labels)
I'd prefer the editor and viewer programs each have separate taskbar icons, irrespective of how they're started.
I'd also prefer that the editor had more distinctive icon, perhaps a little red book rather than a little brown one
I often use Close all on the viewer icon, especially if I see a stack of them grouped together.
BR