Wrong Reply email address

Hi,
I have Support Center Plus installed with three Business Units, I configure the Incoming mail server with an account named supportcenter@***.org, in the Business Unit in the Mail configuration I added the incoming mail address = ITsupport@***.org and in Reply-to-Adreess = ITsupport@***.org, When a representative make a reply int the Request the from mail address shows ITsupport@***.org, but when the user open his email the from email address was changed to supportcenter@***.org, if the user reply the system will create a new request and do not update the request from where the representative did the reply. We are using google mail server, the itsupport@***.org has a forwarding to supportcenter@***.org.
The support team didn't help.