Hmm, I don't think it's a bug but rather a setting in Fences 2. Anyway, here is the screenshot that you asked for :).
dttvinh
That's weird. As far as I can remember, right-button drag has always been the default Fence maker. Well, both left and right-button dragging do the same in Fences 2 beta anyway so there's not much difference. PS: just realize that if I move the mouse away for a while, the "Create Fence from these icons" pop-up will disappear eventually but still, that's kind of annoying :(.
I think the title say it all. I've just upgraded to Fences 2 beta because of the folder portal (and also desktop pages). However, I cannot drag a rectangle to select many items like before because a pop-up window automatically appears and asks me to create another fences with those items. In the past, it only happened when I used my right mouse button, but now...