It appeared that a bug came along for the ride in the TWO theme (as Rex correctly pointed out). The workaround was not extending the TWO theme, but I have now issued a fix that fixes the TWO theme too.
Press CONTROL + F5 in the editor to update Adventuron Classroom to version 28d - the fixed version.
Confirm version number by clicking the "MENU" button at the bottom right of the editor window.
So sorry for the trouble, and the turnaround time for the fix (12 hours). I'm like Clark Ken in the fortress of solitude during the events of Superman II. Yeh, just like that :-)
Chris