If you make the screen smaller the layout changes, but it doesn’t return if you make it bigger again.
It also doesn’t appear to respond at all when the size changes as a result of rotating a device (tested on Android with chrome)
The way responsiveness works also appears to be sensitive to the widths that are set on the columns. For example, in the layout at http://dev2.ubiapps.com/ if I swap the order of the two columns (map and sidebar) it behaves differently. If this is intended, it should be documented.
I set such a gravity in order to make the Accordion column smaller than the Map column (you can use bigger value, 0.1 for example). So, the right column is small, its width can not be less than 310px.