looking inside persistence table, through different Virtual Servers

hmm....

The variable itself seems to be expanding just fine, but I have no idea why the trailing characters are not logged.

It might be worth looking at the output of "b list " to see if those characters are in the config. If the rule looks correct in the config (well really either way), I'd recommend contacting F5 Support to look into the reason for the missing characters in the log command output.

You could try using the MAC value in a slightly different way, I guess. Maybe just checking the last 2 characters in the MAC?

 set fwIP [findclass [getfield $fwMAC ":" 6] $::fw_MAC2IP " "] 

against a modified class:

class fw_MAC2IP {
  10.9.1.11 f7
  10.9.1.12 f8
}

HTH

/deb