states and countries do not get imported into Custom Fields

States/provinces and countries do not get imported from CSV files into Custom Fields (they do get imported into Locations, though).

After creating a Custom Group with two Custom Fields (one State and one Country) I generated a CSV file with two entries, one with mazowieckie, Poland and another with Utah, United States. These values did not get imported into the selected (by matching) Custom Fields. I also tried to replace the states and countries with their numerical representations in CiviCRM database (1300, 1172 and 1043, 1228, respectively), but this approach throws Invalid Row errors (which is correct, as we should expect the states and countries to be expressed as names in the imported files).