There seems to still be some bugs with the Arrange Models feature. I asked for 19 copies of the selected, center model. As you can see, it gave me 19 and arrange them all nicely, except it didn't center them properly and so I ended up with two of them overlapping the first one. I tried a couple of other tests, making 9 copies and then selecting one of them and asking for 10 copies, and got various places where they overlapped.