Outlook 2003 - Message icon doesn't change when msg is read

[Chopsy]

I have a strange issue in Outlook 2003 that is a little annoying. When we get an email from a particular sender, the envelope icon doesn't change from the yellow closed envelope to the open white envelope even after the message is read. The text changes from bold to normal, but no change in the icon.

The message is actually generated from a server based 'auto-responder' rule on the Exchange server (it's our 'helpdesk' account), but I don't see this happen with other auto-responders.

Any ideas?