Theoretically the MapStore.save function should return an indication of whether the saved value was already known or not. This is currently failing with "false" always being the return.
As a consequence, the layergroups are considered new more than they should.
The only reason why they are not is because of a second-level internal LRU cache,
Affects performance because in a clustered environment each process will check new coming POSTs over and over.
Fix MapStore.save always false "known" return variable