Thanks for your investigations. I have an idea. The automatic closing of polygons only closes single ways but does not check if the way could be closed by connecting it to another way. This is a bit tricky and I fear that there might be some side effects. But possibly it works. I will try to implement a patch. WanMil
Thanks Wanmil, I got this message in the log file: c:\Downloads\Benelux\10010046.osm.gz: Cannot join the following ways to closed polygons. Multipolygon http://www.openstreetmap.org/browse/relation/1424029
On my map the Albert canal looks empty, except for the river in the centre. On the adjacent tiles west and east of tile 10010046, the Albert canal is filled with water again, because there the ends of the multipolygon are detected.
I put the log file here: http://mijndev.openstreetmap.nl/~ligfietser/diverse/mkgmap.log.zip