drag objects across dual-screen boundary?

I am using Ubuntu 12.04 on a notebook computer with an external screen. Dual-screen mode works just fine except when dragging objects. When I just move the cursor or drag a window from one screen to the other the cursor stops a short while at the screen boundary and then moves on. It is more or less as if there were a couple of (100?) invisible pixels between the two screens. No problem, maybe it's intentional. (Works as designed?)

Still, when I grab a file in nautilus in order to drag it to another window (e.g., Totem or VLC media player) the cursor stops at the screen boundary much longer. At first I thought it just could not cross the boundary at all but if I keep dragging long enough it will move on. From the way my mouse has to go I estimate the delay to be equivalent to more than 1000 invisible pixels.

Is this behaviour configurable? Many thanks in advance.