row.child().show() not showing child row after destroy()

Test Case: http://live.datatables.net/lokigaku/1/

For each row, if you click the icon, and child row will expand to show more detail which it accesses via Ajax (not included in demo).

This works fine on initial load however, If you select a different month from the dropdown (top left of screen) it redraws the data and then the icons become unclickable. The child row will not appear.

There appears to be a pattern: Every second redraw will not render the child row however, every alternate redraw will make it clickable again...

I can't see where this is falling down (or what I am doing every second time that re-renders it correctly)