[mkgmap-dev] Create different Maps with working routing between them - is it possible?

Folks, if I download two countries pbf from geofabrik, merge them via osmosis and then build a single img map routing works fine across the countries. If I create two img files, one per country and put it on my garmin device, enable both maps, I can see all the ways seems correctly linked but routing across the two countries (maps) fails. Is that the expected behavior or am I doing somehting wrong? Thanks, Enrico