Unable to add multiple recipients in Mail 8 for OS X Yosemite with Contacts interface closing.

[AnAppleADay]

I know how to send to multiple recipients from my Contacts list, however when I click the + icon to the right of the To field or the CC field... I am met with my Contacts list (which is what I want) however I do not have an option to select multiple recipients at once or have the Contacts window (which interfaces with the Contacts application) remain open so I can just scroll through my list and select who I want... I tried to Command+Click the contacts I want and all it does is expand the contact in question and allow to select one, then the Contacts window disappears and I have to continuously go into the Contacts window. Any ideas?

Thanks,

Steve