%{2} not expanding for accounting packets?

[Phil Mayers]

We've got some switches that don't include the MAC address in the 
Calling-Station-Id of accounting packets. To simplify the config, I use 
an unlang expression to add it:

if ((!Calling-Station-Id) && (NAS-Port-Type == Ethernet) && (User-Name 
=~ /(..)(..)(..)(..)(..)(..)/)) {
   update request {
     Calling-Station-Id = "%{1}:%{2}:%{3}:%{4}:%{5}:%{6}"
   }
}

However, the output of that is:

00::22:33:44:55

...which is odd:

rad_recv: Accounting-Request packet from host 172.16.54.36 port 32770, 
id=92, length=113
         Acct-Status-Type = Start
         User-Name = "001E0BA09F67"
         NAS-IP-Address = 172.16.54.36
         Acct-Session-Id = "Tue Jul 29, 2008 18:54:00"
         Service-Type = Login-User
         NAS-Port = 1035
         NAS-Port-Type = Ethernet
         Tunnel-Private-Group-Id:0 = "14"
         Tunnel-Type:0 = VLAN
         Tunnel-Medium-Type:0 = IEEE-802
         Acct-Delay-Time = 0
server macauth {
+- entering group preacct
calling-mac-1: Could not find value pair for attribute Calling-Station-Id
++[calling-mac-1] returns noop
calling-mac-2: Could not find value pair for attribute Calling-Station-Id
++[calling-mac-2] returns noop
called-mac-1: Could not find value pair for attribute Called-Station-Id
++[called-mac-1] returns noop
called-mac-2: Could not find value pair for attribute Called-Station-Id
++[called-mac-2] returns noop
++? if ((!Calling-Station-Id) && (NAS-Port-Type == Ethernet) && 
(User-Name =~ /(..)(..)(..)(..)(..)(..)/))
?? Evaluating !(Calling-Station-Id) -> FALSE
?? Evaluating (NAS-Port-Type == Ethernet) -> TRUE
?? Evaluating (User-Name =~ /(..)(..)(..)(..)(..)(..)/) -> TRUE
++? if ((!Calling-Station-Id) && (NAS-Port-Type == Ethernet) && 
(User-Name =~ /(..)(..)(..)(..)(..)(..)/)) -> TRUE
++- entering if ((!Calling-Station-Id) && (NAS-Port-Type == Ethernet) && 
(User-Name =~ /(..)(..)(..)(..)(..)(..)/))
         expand: %{1}:%{2}:%{3}:%{4}:%{5}:%{6} -> 00::0B:A0:9F:67

Similar expressions in the "authorize" section appear to work.

Anyone have any ideas?