Timeline onMove callback
There is a problem with the onMove callback function which causes the dragged item to return to the wrong group when using callback(null).
This bug seems to only occur when the timeline height is restricted so to enable vertical dragging between groups.
I have briefly looked into it, and I believe it may have something to do with the ItemSet._onDragStart() method being called twice. I have included console messages in the 2 following jsfiddles to indicate this. Note that in the fiddle without the restricted height, onDragStart does not call twice and the bug does not occur.
Steps to reproduce bug:
- Go to the fiddle with the restricted height
- Open up the javascript console
- Drag and drop an item onto the DROP ONTO ME group
- May take a couple of tries, but the item should return to the wrong group
- Also note the console messages indicating the onDragStart method being called twice for each drag operation