I removed my MapInstall 4.2.0 and installed 4.0.4. It does much better than 4.2.0, but despite asking for a full install of a mapset (and it confirming a full install when you run it afterwards), it leaves-out a few segments (apparently the same ones each time).
I'm using OSM maps created by
http://garmin.openstreetmap.nl/. It doesn't matter whether I'm trying to install 2 maps, or just one.
I have been successful in loading maps by copying their img files directly, so that might have to do. However, all the maps that I don't have single img file for are a problem.