It's correct. Kupfer only uses generic exception guards when initializing and during the first uncached load of plugins.
The coverage needs to be expanded to anytime we fetch objects from plugins. This is something that we have to build out step by step, there is no real clean model in Kupfer for this (at the moment). I think that sources call for a redesign anyway (no more instant rescan), and after some redesign of how source caching and reload works, it should be much easier to implement this cleanly.