Odd results with iRule on virtual server selecting random pool member

 
 when CLIENT_ACCEPTED { 
    if { [TCP::local_port] == 80 } { 
       log local0. "accepted" 
       TCP::collect 100 
    } 
 } 
 when CLIENT_DATA { 
    if { [ findstr [TCP::payload] "rand=" 5 4] equals true} { 
       set daStr [ findstr [TCP::payload] "rand=" 5 4] 
       log local0. "rand= found" 
       if { $daStr equals "true" } { 
          set cserver [lindex [active_members -list pool_bookings] [expr {int(rand()*[active_members pool_bookings])}]] 
          set ip [lindex $cserver 0] 
          pool pool_bookings member $ip 
          persist none 
          TCP::release 
          TCP::collect 
       } 
    } 
 }