Called Sprint about this, and got forwarded to HTC. They said I was the first to report this. If you have a similar bug with your EVO / Exchange / ActiveSync / Meeting Invite Response it may be worth referencing HTC ticket: 10USD280004784
Meeting acceptance responses sent from HTC Evo to Exchange 2003 / Outlook 2003 show as being sent from the incorrect user (when there are multiple invitees and the EVO user isn't the first on the list). This occurs when when the user accepts a meeting invite and chooses not to "Edit the response". When a user makes a note within their acceptance response, the acceptance reply appears properly to the meeting creator.
Exchange 2003 (Version 6.5 Build 7638.2: Service Pack 2)
Single server configuration hosting OWA/OMA Services
Meeting Creator Mail Client:
Outlook 2003 (Version 11.8313.8324) SP3
Meeting Invitee Mobile Device
HTC EVO Build - Software number: 1.47.651.1
Device configured to refresch Exchange ActiveSync account every 30 minutes.
Spoke with HTC and they indicated that they were able to recreate the problem within their test environment. They noted that they would get back to me as soon as they had any updates to share concerning the bug.