[c-nsp] monitor session on a LACP port channel?

[William S. Duncanson]

I'm probably missing something really obvious here, but I'm trying to do a
monitor session on a LACP port channel.  sh etherchannel 16 port-channel
says the following:

houcore5#sh etherchannel 16 port-channel
                Port-channels in the group:
                ----------------------

Port-channel: Po16    (Primary Aggregator)

------------

Age of the Port-channel   = 11d:00h:49m:54s
Logical slot/port   = 14/16          Number of ports = 0
HotStandBy port = null
Port state          = Port-channel Ag-Not-Inuse
Protocol            =   LACP
Fast-switchover     = disabled

Time since last port bundled:    11d:00h:49m:19s    Gi9/18
Time since last port Un-bundled: 11d:00h:47m:20s    Gi9/18

Port-channel: Po16C
------------

Age of the Port-channel   = 11d:00h:48m:23s
Logical slot/port   = 14/19          Number of ports = 4
HotStandBy port = null

Doing a "monitor session 1 source interface po16" yields no traffic on the
destination port; not surprising, as the interface is marked down/down.
Po16C is marked as up/up, but "monitor session 1 source interface po16C"
doesn't seem to be acceptable to the command interpreter.  What am I doing
wrong?