Keep encoding when request is handled by irule

Is there any way how to avoid this and keep origin string at the end? I tried to add binary scan to more places but result is still same:

  catch {
    if { $UrlEdit } {
        set editpayload [HTTP::payload]
        #binary scan $editpayload [HTTP::payload]
        #HTTP::payload replace 0 [HTTP::header "Content-Length"] $editpayload
        log local0. "DEBUG: myapp: edit page detected with payload: $editpayload"
        binary scan c* $editpayload 
        binary scan c* throwawayvariable
        binary scan $editpayload @0
        HTTP::payload replace 0 $content_length $editpayload
        log local0. "DEBUG: myapp: payload after binary scan: $editpayload"
        HTTP::release
    }
  }
}