Issue with DnD in IE in containers with scrollbar

[cjolif]

Steps to re-create:

1. Copy the attached file to dojo/tests/dnd
2. Open in IE browser
3. Select an item in "Source 1" container.
4. Click on the scrollbar
5. Drag your mouse

Expected result: Mouse should move to where ever its pointing to without any Avatar. Actual result: Mouse is tagged with an Avatar of the selected item.

Analysis: So far what I have observed is that when a user clicks the scrollbar onMouseDown is fired in all browsers onMouseUp is fired in all other browsers except IE, onMouseUp not firing in IE messes up the this.mouseDown variable in the dojo/dnd package hence unexpected creation of the Avatar.

See also: ​https://connect.microsoft.com/IE/feedback/details/783058/scrollbar-trigger-mousedown-but-not-mouseup