Opera for Linux does not try next ip address in DNS list if the ipv6 fails with TCP RST.
This happened because the server in question was set up with IPv6, but
the web-server not set up to listen on IPv6. The web-server is fixed now.
"All" other browsers try the ipv4-address and the web server failure on IPv6 is unnoticed.

The opera response was :

Du prøvde å gå til adressen http://stats.nordu.net/connections.html, som
er utilgjengelig for øyeblikket. Kontroller at nettadressen (URLen) er
skrevet riktig og prøv så å oppdatere siden.

The version is :
Opera/9.80 (X11; Linux x86_64) Presto/2.12.388 Version/12.16

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The packet trace like this :
o. Time Source Destination Protocol
Length Info
62 4.962597 2001:700:1:0:f894:e1a5:d99d:3239 2001:948:4:6::42
TCP 94 34610 > http [SYN] Seq=0 Win=14400 Len=0 MSS=1440
SACK_PERM=1 TSval=1748911481 TSecr=0 WS=128

Frame 62: 94 bytes on wire (752 bits), 94 bytes captured (752 bits)
Ethernet II, Src: 6c:3b:e5:35:61:ba (6c:3b:e5:35:61:ba), Dst:
Cisco_5d:04:00 (00:1e:79:5d:04:00)
Internet Protocol Version 6, Src: 2001:700:1:0:f894:e1a5:d99d:3239
(2001:700:1:0:f894:e1a5:d99d:3239), Dst: 2001:948:4:6::42 (2001:948:4:6::42)
Transmission Control Protocol, Src Port: 34610 (34610), Dst Port: http
(80), Seq: 0, Len: 0
Source port: 34610 (34610)
Destination port: http (80)
[Stream index: 3]
Sequence number: 0 (relative sequence number)
Header length: 40 bytes
Flags: 0x002 (SYN)
Window size value: 14400
[Calculated window size: 14400]
Checksum: 0x36d7 [validation disabled]
[Good Checksum: False]
[Bad Checksum: False]
Options: (20 bytes)

No. Time Source Destination Protocol
Length Info
63 4.978524 2001:948:4:6::42
2001:700:1:0:f894:e1a5:d99d:3239 TCP 74 http > 34610 [RST, ACK]
Seq=1 Ack=1 Win=0 Len=0

Frame 63: 74 bytes on wire (592 bits), 74 bytes captured (592 bits)
Ethernet II, Src: Cisco_5d:04:00 (00:1e:79:5d:04:00), Dst:
6c:3b:e5:35:61:ba (6c:3b:e5:35:61:ba)
Internet Protocol Version 6, Src: 2001:948:4:6::42 (2001:948:4:6::42),
Dst: 2001:700:1:0:f894:e1a5:d99d:3239 (2001:700:1:0:f894:e1a5:d99d:3239)
Transmission Control Protocol, Src Port: http (80), Dst Port: 34610
(34610), Seq: 1, Ack: 1, Len: 0
Source port: http (80)
Destination port: 34610 (34610)
[Stream index: 3]
Sequence number: 1 (relative sequence number)
Acknowledgement number: 1 (relative ack number)
Header length: 20 bytes
Flags: 0x014 (RST, ACK)
Window size value: 0
[Calculated window size: 0]
[Window size scaling factor: -1 (unknown)]
Checksum: 0xb93f [validation disabled]
[Good Checksum: False]
[Bad Checksum: False]
[SEQ/ACK analysis]
[This is an ACK to the segment in frame: 62]
[The RTT to ACK the segment was: 0.015927000 seconds]

No. Time Source Destination Protocol
Length Info
64 4.978660 2001:700:1:0:f894:e1a5:d99d:3239 2001:948:4:6::42
TCP 94 34611 > http [SYN] Seq=0 Win=14400 Len=0 MSS=1440
SACK_PERM=1 TSval=1748911485 TSecr=0 WS=128