Yeah, if its the same issue then I don't know what to say really, sorry :\ Perhaps you can share the scene with the devs so that they can have a look at it.
The whole bump thing is just plain weird and I don't know what else to say about it. It is unreliable and as you've noticed it gets even more unreliable when you start messing with the projector shader. We don't have UVW nodes in Corona so scaling bump maps is pretty much impossible on certain systems (2S?) unless you are cool with a severe performance reduction or as you've noticed... Bump maps changing their appearance when dealing with different resolutions.
The situation gets even more confusing because from what I can tell this has been present in v5 and probably earlier builds as well. So while I hope the devs fix this thing in the upcoming daily builds, it still remains a problem because dailies are supposed to be broken in weird ways anyway and so if you are running or are relying on an external farm things get super messy with the different versions and features that work in some releases and don't in others.
TLDR, if you have a farm, what do you do? Update the farm for project X with the daily then downgrade the farm to the latest official release for Project Y because the daily is broken in other ways? I'd almost like to say that maybe the official releases should be fewer but more polished out.
Anyway, to end on a positive note, I think we all know that the devs are hard at work at the moment and hopefully these things will be ironed out for whenever v6 gets released. I personally wouldn't mind if they take 3 month more to really polish stuff out and make it production ready. However wants to play around with the latest and greatest can download the daily build anyway :P