I got that one several days ago: unable to save because yadayada the graph dependencies yadayada still in use whatever. Ben’s solution was to close without saving, but when it happened to me, I only needed to recompile an open blueprint to get saving to work again. That would probably count as an Unreal bug (exists in 4.14.3 too, or I might have been using 4.14.2 when it happened).
Edit of course I unpaused and continued watching and Ben’s issue was having two editors open. That’s not a bug in that case…it’s a feature that two copies will fight over the same resources. Though a warning when having two copies open might not be a bad idea, since it’s rare one would want to do this on purpose.