There were no official notes for this release. 

The only documentation we have is an email from the Lucent Beta team:

Release 3.9.1b18 has a DHCP server and NAT, but not IPX.
THIS RELEASE DOES NOT WORK ON THE OR-U-AP with the POTS port.

Release 3.9.1b18 is based on release 3.9b27
It  has less of a memory leak than 3.9b27.  
The leak was most evident when  using MLPPP and not having disabled 
IPX as below.

The IPX module is no longer present in the OR  series when using the 
NAT-enabled builds.

Before upgrading an Office Router to ComOS 3.9.1b18, you MUST disable the
Open Shortest Path First (OSPF) and IPX protocols. To do so, enter the
following commands:

    set ospf disable
    set ipx off
    save all
    reboot

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