The current client-side reporting doesn't work very well. Many error conditions result in unfriendly behavior in the client and a failure to even deliver an error message.
I'm leaving this bug as "assigned" unless there are objections, because there may still be more work to do on it. I don't have time at the moment to do a good analysis of what else should be improved.
*** Bug 887039 has been marked as a duplicate of this bug. ***
Moved to https://pulp.plan.io/issues/353