I also noticed this with the Geofabrik extract of Germany: The tile around Bremen always gets flooded. My tiles are different from yours, so I assume we have different max-nodes parameters.

I did also compile Geofabrik's complete Europe extract: here the problem did not occur. There were a couple of other landlocked tiles in France and Poland which were flooded though (caused by, I assume, some bad data in the tiles).

This may mean, therefore, that the problem stems from the way Geofabrik extracts Germany. You could try making your own extract (using a bounding box) for Germany out of the Europe extract. Perhaps this would work better.

Cheers.