In other words, for a Norwegian PhD, an international postdoctoral experience is not a golden ticket to employment in the Norwegian academy.
However, what the working paper of the Nordic Institute for Studies in Innovation, Research and Education (NIFU) doesn't reveal is the proportion of internationally-mobile Norwegian postdocs who gain continuing faculty employment in another country. (Indeed, for some this may well have been one of the primary motivations for the move abroad.)
Whilst much has been written on faculty/academic mobility (see a recent article focused on Europe, below), the NIFU paper highlights the fact that questions of national brain drain are evidently still to the fore. Yet, academia has long been a site of brain circulation. At what point, therefore, will national governments start in earnest to analyse the benefits from brain circulation, i.e. drain + gain?
The UK did this in 2011 in a government report on the International Comparative Performance of the UK Research Base. This report concluded that UK research is both mobile and international. In a potentially significant finding for Norway, the UK determined that researchers who had returned to the UK after an extended time abroad were significantly more productive in terms of articles published than those who had never left the UK.
Further reading
Van Der Wende, Marijk. 2015. ‘International Academic Mobility: Towards a Concentration of the Minds in Europe’. Research and Occasional Papers Series (ROPS), Center for Studies in Higher Education, University of California, Berkeley, no. CSHE.3.15 (February). http://www.cshe.berkeley.edu/publications/international-academic-mobility-towards-concentration-minds-europe.