Index: src/uk/me/parabola/mkgmap/reader/osm/SeaGenerator.java
===================================================================
--- src/uk/me/parabola/mkgmap/reader/osm/SeaGenerator.java	(revision 1952)
+++ src/uk/me/parabola/mkgmap/reader/osm/SeaGenerator.java	(working copy)
@@ -465,7 +465,16 @@
 					if (clippedWays.size() != clipped.size()) {
 						clipped = new ArrayList<List<Coord>>(clippedWays.size());
 						for (Way w : clippedWays) {
-							clipped.add(w.getPoints());
+							// after joining all ways must now end on the bbox
+							if (w.getPoints().size() > 1) {
+								if (bounds.onBoundary(w.getPoints().get(0))
+										|| bounds.onBoundary(w.getPoints().get(
+												w.getPoints().size() - 1))) {
+									clipped.add(w.getPoints());
+								} else {
+									log.warn("Remove artefact from bbox clipping",w);
+								}
+							}
 						}
 					}
 					log.info(clipped.size(),"joined clippings.");
@@ -479,7 +488,7 @@
 			}
 		}
 
-		log.info("clipping: adding ", toBeAdded.size(), ", removing ", toBeRemoved.size());
+		log.info("clipping: adding", toBeAdded.size(), ", removing", toBeRemoved.size());
 		shoreline.removeAll(toBeRemoved);
 		shoreline.addAll(toBeAdded);
 	}