The extra spaces (it looks like invisible elements) are added at the end of the row while dragging the avatar. It only seems to be occuring in when the browser width is *JUST* big enough to hold the elements in their arangement.
Steps to reproduce:
1) open the generic light box example from the daily build site:
2) adjust the browser size so that it is *JUST* wide enough to hold two full rows and a third row with only 2 elements
3) attempt to drag an element. Notice that the row it is over, has an empty space at the end, which pushes the other elements forward.
4) attempt to drag an element at the end of the row. Notice that there is now a new row created, which is completely blank except for the last element.