The Shutter windows lack distinguishing X roles and instance names

I am trying to configure how Shutter acts in my i3 window manager. I want to specify the main Shutter window, the one with "Session" in the title, but all the windows in Shutter have the same X instance name and class name, and none of them have a role (WM_WINDOW_ROLE) specified.

Currently I'm identifying the main window by checking the title for "Session", but using the title is discouraged.

Ideally, the role or instance for each of the windows should be "session", "preferences", "pop-up" etc. That would make them very easy to identify. So, instead of all the windows showing this line under xprop:

WM_CLASS(STRING) = "shutter", "Shutter"

They should show lines like this:

WM_CLASS(STRING) = "session", "Shutter"
WM_CLASS(STRING) = "preferences", "Shutter"
WM_CLASS(STRING) = "popup", "Shutter"

NB: By popup, I'm referring to the error message box that pops up when Shutter can't grab the keyboard. Screenshot attached.