Does Calendar icon on the left edge supposed to be like that or that a bug ?

i don't know why

It's application icon or icon for Today?
The application icon in menu is fine. It's just the one on the left edge which has this problem.
This is application-x-executable-symbolic.svg icon, and there is no explaining why Calendar using it. I added missing org.gnome.Calendar-symbolic.svg icon, but the app using it in the application menu only. Looks it's GNOME Calendar bug.
@SmartFinn hey, it's me again. It's a gtk bug/issue see here https://bugzilla.gnome.org/show_bug.cgi?id=783217. The default icon is application-x-executable-symbolic. I have requested to use the symbolic icon if found or fallback to a better icon. As for now, apps can't set this icon:/
@bil-elmoussaoui Thanks for the description of the issue. This is really not the best choice for the fallback icon.