I've replicated what the customer was describing. He has made some Contacts with multiple email addresses in the first Email Address block. Lets say the Contact name was "Friends 55"....he would be able to start a New Message, and begin typing Friends55, and once selected, all of those entered email addresses would be in the TO: field (granted all within the same < >). It sends successfully.
Now, when typing it into the TO: field and selecting it, ONLY the first email address in that Friends55 list appears. If you click on the TO: block, you can select "Friends55" from the Recipients List, and ALL of the entered email addresses go into the TO: field. This is great, except you can quickly type to filter within the Recipient list when presented it after clicking the TO: block....which is why most folks just start typing directly and select what's available.
A possible compromise is going into Contacts first and selecting the Contact, then picking Send Email, since that ALSO puts all of the email address in the TO: field as well.
Any chance on having it populate the same way when simply typing into the TO: field and selecting from the resulting filtered list? If not, any chance on adding the ability to type to filter the Recipient List after clicking on the TO: block?
Let us know and we can inform our customer to see if any functional changes have to happen in how Contact lists are created for use in the future...