[c-nsp] destination span rate is lower than source

[Tassos Chatzithomaoglou]

I'm trying to troubleshoot an issue on a 6500/SUP2 and i have noticed that when mirroring a specific port, i'm getting 
less traffic that is actually going out. The source is sending continuously at the same rate and the problem is 
happening all the time.

6500#sh int gi3/24 | i ut rate
   30 second input rate 83000 bits/sec, 137 packets/sec
   30 second output rate 284000 bits/sec, 191 packets/sec

6500#sh int gi3/29 | i ut rate
   30 second input rate 0 bits/sec, 0 packets/sec
   30 second output rate 54000 bits/sec, 85 packets/sec

6500#sh monitor session 13
Session 13
----------
Type              : Local Session
Source Ports      :
     RX Only       : Gi3/24
Destination Ports : Gi3/29

Port Gi3/24 is a trunk port and Gi3/29 is a routed port (i have tried switchport and with trunk too).

I have checked traffic of ports 3/24-3/31 and the total is quite low.

GigabitEthernet3/24 is up, line protocol is up (connected)
   30 second input rate 83000 bits/sec, 138 packets/sec
   30 second output rate 284000 bits/sec, 190 packets/sec
GigabitEthernet3/25 is up, line protocol is up (connected)
   30 second input rate 6000 bits/sec, 6 packets/sec
   30 second output rate 21000 bits/sec, 30 packets/sec
GigabitEthernet3/26 is up, line protocol is up (connected)
   30 second input rate 0 bits/sec, 0 packets/sec
   30 second output rate 0 bits/sec, 0 packets/sec
GigabitEthernet3/27 is up, line protocol is up (connected)
   30 second input rate 0 bits/sec, 0 packets/sec
   30 second output rate 0 bits/sec, 0 packets/sec
GigabitEthernet3/28 is up, line protocol is up (connected)
   5 minute input rate 0 bits/sec, 0 packets/sec
   5 minute output rate 11000 bits/sec, 19 packets/sec
GigabitEthernet3/29 is up, line protocol is down (monitoring)
   30 second input rate 0 bits/sec, 0 packets/sec
   30 second output rate 54000 bits/sec, 86 packets/sec
GigabitEthernet3/30 is up, line protocol is up (connected)
   5 minute input rate 138000 bits/sec, 38 packets/sec
   5 minute output rate 95000 bits/sec, 39 packets/sec
GigabitEthernet3/31 is up, line protocol is down (notconnect)
   5 minute input rate 0 bits/sec, 0 packets/sec
   5 minute output rate 0 bits/sec, 0 packets/sec

module 3 is a WS-X6148-GE-TX, 6500/SUP2 runs 12.1(26)E9 and the cpu load is around 5%.

Is there a case the extra traffic could be dropped somewhere after being counted on the port and before going into span?
Checking for errors didn't return anything too.

-- 
Tassos