This can be reproduced by modifying the 'Drop Based Coding' example (http://developer.yahoo.com/yui/3/examples/dd/drop-code.html) as follows:

• Change #drop style of 'right: 5px' to 'left: 5px'
• Add 'dd-constrain' to the use list
• Change dd declaration to:

<code>
var dd = new Y.DD.Drag({
node: v,
dragMode: 'intersect',
data: thisData
}).plug(Y.Plugin.DDConstrained, {
constrain2node: '#play',
stickY: true
});
</code>

Drag one of the nodes down to intersect over the drop box but keep your mouse cursor far out to the right (use _debugShim to ensure the cursor is outside of the drop's shim). The dragged node will
intersect the drop box without the drop changing color. If you then bring your mouse cursor inside the drop's shim, it changes color.