Strange iRule behavoir v9.4.8

Greetings -

Recently we had some strange behavior and I'd like to get some opinions on the cause...

We have 3 iRules applied to a virtual server and one supporting class:

rule strip_xforwardedfor {
   when HTTP_REQUEST {
     while { [HTTP::header exists X-Forwarded-For] } {
       HTTP::header remove X-Forwarded-For
     }
  }
}
rule add_xforwardedfor {
  when HTTP_REQUEST {
    HTTP::header insert X-Forwarded-For [IP::client_addr]
  }
}
rule redirect_by_host_and_uri {
   when HTTP_REQUEST {
  foreach row [lsort -decreasing -index 1 $::host_uri_redirector_class] {
    if { [string tolower [HTTP::host]] equals [getfield $row " " 1] }{
      if { [string tolower [HTTP::uri]] starts_with [getfield $row " " 2] }{
        HTTP::redirect [getfield $row " " 3]
        break
      }
    }
  }
 }
}
class host_uri_redirector_class {
   "www.example.com /foobar http://foobar.example.com"
}

There are a whole host of reasons we use these rules, but we do use X-Forwarded-For to restrict access to some services, so it's necessary to remove existing and re-add them. We also have a lot of fingers in the LTM with varying degrees of experience, so it made sense for use to have people edit a class rather than develop iRules.

We have a standard http vserver with something special:

virtual test_vserver {
   snat automap
   destination 111.111.111.111:http
   ip protocol tcp
   rules
      strip_xforwardedfor
      add_xforwardedfor
      redirect_by_host_and_uri
   profiles
      http
      tcp
}

I originally had the rules in the order:

redirect_by_host_and_uri

strip_xforwardedfor

add_xforwardedfor

because it made sense to me that we wouldn't want to bother processing X-Forwarded-For if we were just going to redirect somewhere... This resulted in a connection reset from Windows (XP) only -- on many different workstations both internal and external with both Firefox and IE. It also resulted in these errors in /var/log/ltm

Apr 15 13:56:23 tmm tmm[1895]: 01220001:3: TCL error: strip_xforwardedfor  - Operation not supported (line 2)     invoked from within "HTTP::header remove X-Forwarded-For"
Apr 15 13:56:23 tmm tmm[1895]: 01220001:3: TCL error: strip_xforwardedfor  - Operation not supported (line 2)     invoked from within "HTTP::header remove X-Forwarded-For"
Apr 15 13:56:24 tmm tmm[1895]: 01220001:3: TCL error: strip_xforwardedfor  - Operation not supported (line 2)     invoked from within "HTTP::header remove X-Forwarded-For"
Apr 15 13:56:25 tmm tmm[1895]: 01220001:3: TCL error: strip_xforwardedfor  - Operation not supported (line 2)     invoked from within "HTTP::header remove X-Forwarded-For"
Apr 15 13:56:26 tmm tmm[1895]: 01220001:3: TCL error: strip_xforwardedfor  - Operation not supported (line 2)     invoked from within "HTTP::header remove X-Forwarded-For"
Apr 15 13:56:26 tmm tmm[1895]: 01220001:3: TCL error: strip_xforwardedfor  - Operation not supported (line 2)     invoked from within "HTTP::header remove X-Forwarded-For"
Apr 15 13:56:27 tmm tmm[1895]: 01220001:3: TCL error: strip_xforwardedfor  - Operation not supported (line 2)     invoked from within "HTTP::header remove X-Forwarded-For"

However, with the redirect rule moved to the bottom... all is well. No errors, no connection resets. This always worked in both OSX and Linux.

I also tried changing the xforwardedfor rules to be clientside only and received the same errors.

Thoughts?