Hi Fabien, that's due to a bug in Mac Rhino V6 where it does not support the Mac Rhino V5 clipboard format that both MoI and Rhino v5 uses.

You can see the bug using Mac Rhino v5 to Mac Rhino v6 too, if you run Rhino v5 and select an object and copy it to the clipboard, then exit Rhino v5 and launch Rhino v6 and try to paste it in nothing happens.

There is a Rhino bug open for this: https://mcneel.myjetbrains.com/youtrack/issue/RH-57560 .

I have a workaround that will work with the next MoI v4 beta though, if you e-mail me I will send you a test to see if it works ok.

- Michael