I wrote a small proposal for this that can be turn into a PLIP:
only a minor change: we could focus on Plone >= 5.1 instead of Plone 5.0.
It is even possible to produce pointless error message trying to add resources and bundles manually
Sorry but Plone is not a Digital Experience, it's a miserable Experience at the moment.
-aj
Not related to the original problem but here is another case how to wreck the resource registries in Plone 5.0.5 with some simple clicks:
maybe @ebrehault can help here, the last changes are from him, if I'm right: https://github.com/plone/Products.CMFPlone/commit/398cebbbdc7451cfbd8ebba678e65b33376613ea
I have problems with this too, my icons are gone and i have no idea how to reset this 