Why do constant SD nodes not set the IROrder?

Specifically I would like to understand why ConstantSDNode and ConstantFPSDNode do not set the IR ordering like most other SDNode-s. These constant SD nodes also previously did not set the debugloc, but that got enabled (here: http://llvm.org/viewvc/llvm-project?view=revision&revision=237237).

These constant SD nodes hard-code the order to 0. Is this intentional, or just something that has not been handled yet? I have a case for debug support where I think this is needed.