Reply-address incorrect format

One user in my organisation has a problem with his e-mail reply-address coming up all wrong at the recipient.
His primary address in Exchange is "firstname.lastname@domain.no", his display name is "Lastname, Firstname" (i don't know whether it matters, I just feel there might be a connection).

When sending to me, the "From" field in my Outlook just displays "Lastname", not the correct display name.

If I try to reply, Outlook tries to reply to "Lastname", which isn't a valid e-mail address at all. But it's still underlined in Outlook.

When we tried sending a message to my private pop-account it had added my providers domain name, ie: lastname@myprovider.no

I've checked the Exchange attributes/Display name on the user in AD, but didn't find anything out of the ordinary.

See below for an exerpt of the view-->Options on the message.

Note the "From" section, where the it has split the display name and corresponding address in two, with the undesired result.
The same happens if he sends the message using OWA in stead of Outlook.

I edited out some of the info, and changed domainnames and IPs. Let med know if you need more info.

Thanks

Roger

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Microsoft Mail Internet Headers Version 2.0
Received: from host.domain.local ([xxx.xxx.xxx.xxx]) by mail.domain.no with Microsoft SMTPSVC(6.0.3790.3959);
       Tue, 15 Apr 2008 12:14:07 +0200
Received: from 10.46.40.5 by host.domain.local (InterScan VirusWall 6); 15.
      april 2008 12:14:06
Content-class: urn:content-classes:message
Subject: Test 4
Date: Tue, 15 Apr 2008 12:14:06 +0200
Message-ID: <849B85688634EF44A6C950C060E00A7B68BF1D@host.domain.local>
MIME-Version: 1.0
Content-Type: multipart/mixed;
      boundary="----=_NextPartTM-000-3ea92530-3b5e-44c8-a350-b545e8c84d89"
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
Thread-Topic: Test 4
X-MIMEOLE: Produced By Microsoft Exchange V6.5
Thread-Index: Acie4XAIt3jFQUC2TrS3Pvc9HKRjAA==
From: "Lastname" <Lastname>;
      "Firstname" <firstname.lastname@domain.no>
To: "me@mydomain.no" <me@mydomain.no>
X-TM-AS-Product-Ver: SMEX-7.5.0.1166-5.0.1023-15850.006
X-TM-AS-Result: No--5.022000-4.000000-31
X-TM-AS-Category-Info: : 31:0,000000
X-TM-AS-MatchedID: : 147015-111604-188119-111605-111602-700622-188134-700264
      -111608-188057-111603-111601-148039-148051
Return-Path: firstname.lastname@domain.no
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