I'm using ubuntu gnome 14.10 and gnome shell 3.14.3, the first time I tried to install gloobus-sushi after gloobus-preview package will also remove ubuntu-gnome-desktop package. Check attachment for screenshot.
I think you're probably using the WebUpd8 PPA, so I'm assigning this bug to Andrew.
Which removes gnome-sushi when gloobus-sushi is installed. Unfortunately that's the way it works... I assume "ubuntu-gnome-desktop" is a meta package (which depends on gnome-sushi) so it shouldn't be a problem removing it though of course, that's not ideal, but I don't know how else this could be solved.
Also, where does the "ubuntu-gnome-desktop" package comes from? It's not in the official Ubuntu repositories and I can't find it in the GNOME 3 PPAs either. What's the output of "apt-cache policy ubuntu-gnome-desktop"?
Ah, yes, it is from the Ubuntu repos. Sorry, my bad.
I checked the package and indeed, it depends (doesn't just simply recommends) gnome-sushi. Which is weird, for instance, the ubuntu-desktop meta-package doesn't enforce depends and you can remove non-important apps installed by default without removing the meta package.
Unfortunately, this means that you can't install gloobus-preview without removing gnome-sushi and thus, ubuntu-gnome-desktop. This can only be fixed by the Ubuntu GNOME devs, by moving gnome-sushi from "depends" to "recommends".