Persist iRule based on URI

Oh, yep. That is a bug. Using direct pool member selection doesn't cause a persistence record to be created (or a persist cookie to be inserted). You can add the persist record in an LB_SELECTED event like so (I've also made a few other optimizations):

when HTTP_REQUEST {
   switch -glob [URI::decode [string tolower [HTTP::uri]]] {
   *gb=1* {
         pool webpool member 1.1.1.1 80
         set need_add_persist 1
      }
   *gb=2* {
         pool webpool member 2.2.2.2 80
         set need_add_persist 1
      }
   *gb=3* {
         pool webpool member 3.3.3.3 80
         set need_add_persist 1
      }
   *gb=4* {
         pool webpool member 4.4.4.4 80
         set need_add_persist 1
      }
   *gb=* {
         persist none
         log "Persist Turn Off"
      }
   }
}
when LB_SELECTED {
   if {[info exists need_add_persist]} {
      persist add source_addr [IP::client_addr] 1800
      unset need_add_persist
   }
}