Nvidia config tool config order of screens doesn t work

after installing 2 Nvidia Gforce 650er cards (2 cards with 2 displays) and the driver from my 4 displays are active and everything is fine.
My question:
the option to configure the displays using the mouse to move the screens in the right order doesn t work like under windows with simple moving. Sometimes it is possible to change the order but sometimes it isn t possible to move a screen between 2 others.
Any hints how to solve this?