I display a tree from which only some items must be
draggable, so I couldn't use the default D&D behaviour and had
to reproduce it all by myself (using mousedown, mousemove, ...).
It's working fine except that every time I try to drag a
multiple selection, the multiple selection is lost.
Actually when the tree isn't set with dragEnabled to true, on
mouse down a new selection process is launched (when dragEnabled is
set to true, a new selection process is launched only if you're not
clicking inside the current selection or on mouseup).
Change event isn't cancellable so I don't know how to prevent
the selection to be lost when the user click on it in order to drag