AdvancedCache.getGroup(groupKey) returns all the keys that belong to a group.

If the originator is not an owner, the command is forwarded to the primary owner. If the originator is a primary or a backup owner for the group key, the command is executed locally.

During state transfer, a node may be a write owner for the group key but not a read owner. Currently GroupingInterceptor uses LocalizedCacheTopogy.isWriteOwner(groupKey) instead of isReadOwner(groupKey), so it executes the command on the originator instead of forwarding it to the primary owner.