The Keylab 61 MKII is currently not working 100% in Studio One 4.5, the problem resides with the plugin feedback that Arturia's synths provide the Keylab, it doesn't consistently work without a workaround. I've been working with Arturia to fix it's current state and am hoping that they develop a script so we can use it natively in Studio One. Fingers Crossed..
The keyboard does work otherwise, the plugin feedback is the only thing that appears broken. However, that integration is one of the main reasons to use the Keylab MKII and I think Arturia realizes that.