Resizable containment stops working when helper is defined

I have a div that is resizable and is inside a bigger div which is the containment element defined. When I resize the div outside the containment box nothing happens, as predicted (size is restricted by containment box)

When I also define an helper class the containment stops working as the size is not restricted by the containment box. If you try to resize it outside the containment box my div is resized without constraint.

Examples:

Working ok:

http://jsbin.com/ivevad/2/

Not working correctly:

http://jsbin.com/ocezic/2/

In both of them, try to resize horizontally past the containment box (red border).