[Unbound-users] No failover in stub-zone?

[lst_hoe02 at kwsoft.de]

Hello

we have on our border dns recursor (unbound 1.4.17) some stub-zones  
mostly for PTR lookups for our internal AS112 addresses like this:

stub-zone:
   name: "10.in-addr.arpa"
   stub-addr: <IP-first-internal-NS>
   stub-addr: <IP-second-internal-NS>

Today the first internal NS went down and most reverse lookups slow to  
crawl. I expexted unbound would notice the failure and simply only use  
the second after some time like it did with normal lookups when  
skipping unavailable NS.

Is this expected behaviour or have i done something wrong?

Many Thanks

Andreas