Hallo at all,
in some cases r-3676 (and also earlier releases) generate a wrong preview.img. But tdb-file is always okay.
My way is : first i generate all tiles from the europe-latest.osm.pbf . This makes  no problems; and second i arrangiere some tiles to countries and for those contry-tiles and additionally Contourline-tiles I run a batch to generate the preview and tdb.
My example : first i use 2 tiles 50000002.img and 50000779.img (Island) ; r-3676 generate the preview+tdb, all okay.
second : this 2 tiles and additionally a third tile(Contourlines) : r-3676 generate a wrong preview. This wrong preview is in Mapsource and also in Mapinstall . It makes no different, if the contourline-tile is inside or ouside the other tiles. What is wrong with mkgmap ?  All sourcefiles for evaluation can you download : http:\\img2ms.de\Downloads\Test.rar. I assume  the reason is the actual see.zip or bounds.zip ? 4 months ago with older see and bounds was not this error.
Screenshot preview okay :

Screenshot wrong preview.img :

regards thomas