Before choosing the recipients you should fill in the rest of the meeting request INCLUDING the Location.
When entering the meeting attendees, instead of typing names in directly you hit the TO: button to bring up the address book. From there you need to add the names to the Resource field instead of required or optional. Names/email addresses not in your address book will need to be added manually.
The "Required" field is like the TO: field
The "Optional" field is like the CC: Field
The 'Resource" field is like the BCC: Field
Once you have all the names entered and hit OK it will ask you if you want to populate/change/update the location field with the names you selected. Answer NO to this option then you can hit send. If you say yes accidentally and the names show up in the location field you will need to make sure to change it before you hit send.