static snat assignment not working as expected

I'm trying to do a static SNAT assignment for a virtual server based on the client's source IP address. I'm using the following iRule to do this:

when RULE_INIT {
     Use a local array to configure SNAT addresses.
     These addresses must be defined in a SNAT pool.
     Follow the pattern of the existing addresses to add more than three.

    set static::snat_ips(0) 10.x.y.253
    set static::snat_ips(1) 10.x.y.254

}

when CLIENT_ACCEPTED {
     Restrict port access to HTTP or HTTPS
     If it's a valid port, assign a SNAT entry and allow the connection to continue.
     if it's not a valid port, reject the connection.

    if { ( [TCP::local_port] == 80 ) or
         ( [TCP::local_port] == 443 ) or

             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]}])
        }
    else {
        reject
    }   
}

At this point in time, I'm the only client using the virtual server with this iRule, and in fact I have a tcpdump running that verifies that no one else is using this virtual server. But when I look at my snat translations in TMSH, I see that both of the SNAT IPs are being assigned.

sho ltm snat-translation 10.x.y.253

-----------------------------------
Ltm::SNAT Translation: 10.x.y.253
-----------------------------------
Traffic                ServerSide
  Bits In                  907.7K
  Bits Out                   3.0M
  Packets In                  439
  Packets Out                 410
  Current Connections           3
  Maximum Connections           3
  Total Connections             3


sho ltm snat-translation 10.x.y.254

-----------------------------------
Ltm::SNAT Translation: 10.x.y.254
-----------------------------------
Traffic                ServerSide
  Bits In                  688.0K
  Bits Out                   1.1M
  Packets In                  217
  Packets Out                 168
  Current Connections           0
  Maximum Connections           3
  Total Connections            10

Does anyone have any idea why this would be happening? I would expect my source IP address to always be assigned the same SNAT entry. I cleared the SNAT counters while my TCPDump was running and I verified that the only client IP address that accessed this virtual server after that point in time was my IP address.

Any help would be greatly appreciated.

Thanks, Robert