After sleeping over things, I do not want to doctor in this area anymore. I filed a bugreport regarding the problems a while ago on the JSF2.1 side
and it should be resolved on protocol level by further extensions to our viewstate handling specification on the ppr protocol.
(including client ids for the viewstate forms)
I have to add, cross form submit are already properly resolved by resolving forms which are related to the render cycle, so we have a workaround (although incompatible to mojarra which has non working fixup code) to the problem. So any further work on this issue, without getting the spec changes needed to fix it once and forall is pointless.