[Tilesathome] Mixed tiles rendered incorrectly and a couple of other questions

Hi everyone,

I have observed that some mixed tiles (sea or rivers and land) screw up (not randomly, but consistently on every re-render).
Take a look here:
http://www.informationfreeway.org/?lat=9.982127571086878&lon=105.8568767334366&zoom=12&layers=0B00F000
There's a river with a riverbank and some tiles are just fine but some obviously think they are sea tiles. How to fix that?
Water's always on the "right" side. This also happens with coast areas without riverbanks/islands and also with islands in the sea.

Yesterday I noticed that there are new commands available on informationfreeway.org with which I assume you can mark tiles as sea, land or mixed. Is this mentioned/explained anywhere? I don't see any effect, though. Plus the marking score seems to increase by 0.1 from tile to tile. Does this make sense?

Another question: how to mark green riverbanks/islands? I used the following:
landuse:forest
layer:1
name:somename
Is this correct? But if there's no forest, just green, what value to use?

How to name cities with international names in PotLatch? I read that one should use name.en or name:en but I think PotLatch is buggy there.

Mapnik seems to have some coastline data. Why is this not available in the OSM data? It's quite tedious to do the coastline and knowing it's already there (although maybe not as exact as you could do it by hand or satellite, but it would be a good start).

If my questions are already answered on the web I'm happy with a link :)

Best regards,
Mark