Okay, if ‘Turn on control points…’ is unchecked, I can osnap the corners of a rectangular light. Thats better, but still not what i`m missing from Rhino 5.
There the osnap of an rectangular light was the same like for a rectangular curve. Means. doesn´t matter, on which side I was clicking, osnap got the border of the light.
I think it´s the ‘mid’ or ‘near’ osnap which is not working