Just installed Yosemite (and so far regretting it)… But Xcode acts strange. I have 3 monitors connected.
If I open TWO projects, and move the window of one project to another monitor, then click on that window… it goes full screen AND turns OFF the other two monitors… then I have to figure how to get control back again.
If I put different apps on each monitor, everything works as expected…
turns out its NOT “XCode”… but Yosemite changed what the “GREEN BALL” does! (I don’t like it 
)
Yepp, green ball is fullscreen in Yosemite.
However, hold down Alt while pressing it and it will act like previous systems. 
You can also double click the title bar instead of Option + Click the green ball.
or better yet There is a free app called “Better Touch Tools” that puts it back the way it was…
What I’d like to know… is what % of users would be useing FullScreen, vs MaxWindow? I NEVER clicked that double arrow head before…
http://www.groovypost.com/howto/fix-os-x-yosemite-windows-handling/
Usually I prefer max window.
I only use full screen when running Windows with Parallels.