Using: Viking 1.6.2
Files written by Viking using Export to World File on a Georef layer cannot be correctly read back by Viking using automatic or manual loading of a World File. I think this is because the parameters are in the wrong order when Viking writes the World File.
Viking reads World Files correctly as x_scale, ignore, ignore, y_scale, x_coord, y_coord. But it seems to write World Files incorrectly as x_scale, y_scale, 0, 0, x_coord, y_coord.
Thanks for reporting this and indeed your analysis is correct.
A fix has been applied to the latest source code.