Multiple Open Scores opening separate Windows instead of Tabs

Hello,

As I recall, when I used to use MS-3, if I had multiple scores open, they would open in multiple tabs, within one window.

But every since I've upgraded to MS-4, if I have multiple scores open all at once, each score is opened in a separate window. So, if I use command Tab on my Mac, it shows as if there are multiple MS-4 apps open and same is seen in the doc.

Am I missing a setting?

Thanks.