some question about dig command

[shen Jason]

I uses command "dig www.unitedstatesvisas.gov +trace" to trace dns resolve 
process,but when I use dig version 9.3.2,appear  below:
dig www.unitedstatesvisas.gov +trace

; <<>> DiG 9.3.2 <<>> www.unitedstatesvisas.gov +trace
;; global options:  printcmd
.                       89698   IN      NS      D.ROOT-SERVERS.NET.
.                       89698   IN      NS      E.ROOT-SERVERS.NET.
.                       89698   IN      NS      F.ROOT-SERVERS.NET.
.                       89698   IN      NS      G.ROOT-SERVERS.NET.
.                       89698   IN      NS      H.ROOT-SERVERS.NET.
.                       89698   IN      NS      I.ROOT-SERVERS.NET.
.                       89698   IN      NS      J.ROOT-SERVERS.NET.
.                       89698   IN      NS      K.ROOT-SERVERS.NET.
.                       89698   IN      NS      L.ROOT-SERVERS.NET.
.                       89698   IN      NS      M.ROOT-SERVERS.NET.
.                       89698   IN      NS      A.ROOT-SERVERS.NET.
.                       89698   IN      NS      B.ROOT-SERVERS.NET.
.                       89698   IN      NS      C.ROOT-SERVERS.NET.
;; Received 340 bytes from 127.0.0.1#53(127.0.0.1) in 14 ms

dig: couldn't get address for 'D.ROOT-SERVERS.NET': not found
but when I use dig version 9.2.1,it's ok. whether is the dig version 9.3.2  
had a bug?

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