Hi Goran, I believe the default sorting for an attribute depends on how the underlying database sorts the column to which the attribute is mapped (i.e. if it is string/varchar it sorts alphabetically, if it is integer it sorts numerically).
And there is a way how to override the sorting of an attribute in GoodData - you can define another column in the same database table by which the attribute will be sorted. This column even does not need to be represented in the data model by its own attribute or label.
To do it in the modeller click those three dots next to the attribute (they only appear if you move the mouse over it), then click “Sort by…” and select which column to use for sorting. You can also change sorting order - descending or ascending.