SNAT statistics and iRule for selecting SNAT IP

Hi, I am trying to setup Exchange 2010 via the BigIP utilizing a SNAT pool.

Following the iApp from [1] and the deployment guide linked there [2] I am using the following iRule to ensure SNAT address persistence together with a SNAT pool:

when RULE_INIT {
 Use a local array to configure SNAT addresses.
 These addresses must be defined in a SNAT pool to ensure TMM
 sends gratuitous ARPs during a failover.
 In this example, we use three addresses. Replace
 these with the IP addresses used in your SNAT Pool.
 Follow the pattern of the existing addresses to add more than three.
set static::snat_ips(0) 10.0.0.1
set static::snat_ips(1) 10.0.0.2
set static::snat_ips(2) 10.0.0.3
}

when CLIENT_ACCEPTED {
 Calculate the crc32 checksum of the client IP.
 Use the modulo of the checksum and the number of SNAT IPs in the array
 to select a SNAT IP address.
snat $static::snat_ips([expr {[crc32 [IP::client_addr]] % [array size static::snat_ips]}])
}

The SNAT pool contains the three addresses, that are used like in the example above. This works quite good but if I take a look at the statistics of the SNAT (Statistics ›› Module Statistics : Local Traffic ›› SNAT Translations) nothing shows up. It seems like when using the iRule for selections statistics were not updated.

Is this a bug or expected behaviour? If expected, can I somehow update the statistics from within this iRule somehow?

Cheers, Torsten

[1] http://support.f5.com/kb/en-us/solutions/public/13000/400/sol13497.html

[2] http://www.f5.com/pdf/deployment-guides/microsoft-exchange-2010-2013-iapp-dg.pdf