Rooms and groups
It is hard to tell without inspecting the model. I am using the same version you are using and trying to replicate the error you have there was not possible no matter how I grouped them. There is something in the groups you have there which Revit is not digesting...I skimmed through the release notes of the update but couldn't pick up anything which could have caused that...PS: By the way you can edit a nested group without editing the parent...
Apart from the above I would like to emphasize that there is absolutely nothing wrong with nesting groups as long as one understand the dependencies between Revit element, knows how groups function, which elements to group together and what type of groups are nest-able and which aren't. We have used nested groups on both hospital and hotel project and never had issues at all.
