anchor.diff:  
       // Merge agent
       let mergeAgent =
  -        let timerFactory = self.TimerFactory
  -        let cache = new ExpiringDictionary<XUri, int>(timerFactory)
  +        let cache = new ExpiringDictionary<XUri, int>(timerFactory, false)
           cache.EntryExpired.Add <|
               fun args ->
                   let prUri, retry = args.Entry.Key, args.Entry.Value
  
positive.code:             let rec loop (cache : ExpiringDictionary<XUri, int>) = async {
                  let! msg = inbox.Receive()
                  cache.Set(msg, 0, mergeTTL)
                  return! loop cache
              }
              loop(cache)
  
      // Polling agent
      let pollAgent =
          let timerFactory = self.TimerFactory
          let cache = new ExpiringDictionary<XUri, int>(timerFactory)
          cache.EntryExpired.Add <|
              fun args ->
                  let prUri, retry = args.Entry.Key, args.Entry.Value
  
negative.code:             let rec loop (cache : ExpiringDictionary<XUri, int>) = async {
                  let! msg = inbox.Receive()
                  cache.Set(msg, 0, mergeabilityTTL)
                  logger.DebugFormat("Queued '{0}' for mergeability check in '{1}'", msg, mergeTTL)
                  return! loop cache
              }
              loop(cache)
  