As the title suggests, this is an article about the issue that you may encounter while using SDK 3.x and AdvancedDataGrid.
Unlike other list based components like TileList , DG etc, vertical scroll bar doesnt moves automatically to the last of the row item while drag/drop onto the ADG.
This can be an issue when you have a situation [and most of the time , it can be ] when you have only few visible rows and you want to drag and drop a row /item somewhere in that ADG , not necessarily between the current visible set , you expect that Scroll should move till the last row on its own. In ADG it does not happens , because of one bug which have been already logged here.
https://bugs.adobe.com/jira/browse/FLEXDMV-2471 — if you want to vote/keep a watch on to it.
Workaround is :

change this line
if (collection)
dragScroll();
To
if (collection)
if (dragScrollingInterval == 0)
dragScrollingInterval = setInterval(dragScroll, 15);