MME releases mme-ue-s1ap-id too soon

[spencersevilla]

I've found two unrelated (I think?) instances wherein the MME sends an error [RadioNetwork-cause=unknown-mme-ue-s1ap-id] when it shouldn't.

Case 1:
eNB -> MME: DetachRequest
eNB <- MME: UE ContextReleaseCommand

• waits 1 second *
  eNB -> MME: UE ContextReleaseComplete
  eNB <- MME: (Unknown MME UE s1ap ID)

Case 2:
eNB <- MME: InitialContextSetupRequest, Atach Accept
eNB -> MME: InitialContextSetupFailure (cause=unspecified)
eNB -> MME: UEContextReleaseRequest (cause=unspecified)
eNB <- MME: (Unknown MME UE s1ap ID)

I haven't looked at the 3gpp spec yet but since these eNBs are commercial-grade I assume we are just releasing mme-ue-s1ap-id too soon.