On the Flex SMS Board, with Period View checked. Select a class to copy. Press Copy Class button. If there is no empty cell to click on (the Flex Period + Teacher), the copied class doesn't display. If the cell already has a class in it, nothing happens.

Discovered in this case scenario: an elementary school with only one Flex Period, trying to copy an existing class.

The workaround already exists: un-check Period View. Then a copied class can be put into the same Flex Period with the same teacher or into a different Flex Period with a class already there.