Calculation formulas are not properly restored, since they are not "normalized" (generating an Error in the gradebook).

In backup/backuplib.php the following code:

// use [idnumber] in calculation instead of giXXX#
fwrite ($bf,full_tag("CALCULATION",5,false,$grade_item->get_calculation()));

does not have a correspondance in backup/restorelib.php

I suppose that the set_calculation(...) function must be called somewhere.