Comment 7 for bug 1204896

Yes, the missing librsvg2-common must have been the reason. That package wasn't on our radar before, but I see now we have only a suggest dependency via libgtk-3-0. I could imagine a fresh Kubuntu not having it. If you'd like to confirm this, yes please, try a new VM.
In any case, we better add that package as a direct dependency of Onboard.