Line 2687 reads:
$category->name = get_string('uncategorised', 'grades');
which uses the string 'uncategorised'
where as lines 2115 and 2390 use the defined variable UNCATEGORISED
I think we should be consistent and would recommend changing line 2687 to:
$category->name = get_string(UNCATEGORISED, 'grades'); (this is what Jeff has in GBPv2 but it is different in CVS for 18STABLE.