Index: trunk/src/org/openstreetmap/josm/data/osm/DataSet.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/osm/DataSet.java	(revision 7012)
+++ trunk/src/org/openstreetmap/josm/data/osm/DataSet.java	(revision 7013)
@@ -194,5 +194,5 @@
      * Sets the API version this dataset was created from.
      *
-     * @param version the API version, i.e. "0.5" or "0.6"
+     * @param version the API version, i.e. "0.6"
      */
     public void setVersion(String version) {
Index: trunk/src/org/openstreetmap/josm/gui/layer/OsmDataLayer.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/layer/OsmDataLayer.java	(revision 7012)
+++ trunk/src/org/openstreetmap/josm/gui/layer/OsmDataLayer.java	(revision 7013)
@@ -395,10 +395,7 @@
         }
 
-        // copy the merged layer's API version, downgrade if required
+        // copy the merged layer's API version
         if (data.getVersion() == null) {
             data.setVersion(from.getVersion());
-        } else if ("0.5".equals(data.getVersion()) ^ "0.5".equals(from.getVersion())) {
-            Main.warn(tr("Mixing 0.6 and 0.5 data results in version 0.5"));
-            data.setVersion("0.5");
         }
 
Index: trunk/src/org/openstreetmap/josm/io/OsmReader.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/OsmReader.java	(revision 7012)
+++ trunk/src/org/openstreetmap/josm/io/OsmReader.java	(revision 7013)
@@ -121,5 +121,5 @@
             throwException(tr("Missing mandatory attribute ''{0}''.", "version"));
         }
-        if (!("0.5".equals(v) || "0.6".equals(v))) {
+        if (!"0.6".equals(v)) {
             throwException(tr("Unsupported version: {0}", v));
         }
@@ -468,13 +468,4 @@
                 }
                 break;
-            case "0.5":
-                if (version <= 0 && !current.isNew()) {
-                    Main.warn(tr("Normalizing value of attribute ''version'' of element {0} to {2}, API version is ''{3}''. Got {1}.", current.getUniqueId(), version, 1, "0.5"));
-                    version = 1;
-                } else if (version < 0 && current.isNew()) {
-                    Main.warn(tr("Normalizing value of attribute ''version'' of element {0} to {2}, API version is ''{3}''. Got {1}.", current.getUniqueId(), version, 0, "0.5"));
-                    version = 0;
-                }
-                break;
             default:
                 // should not happen. API version has been checked before
@@ -486,11 +477,4 @@
             if (!current.isNew() && ds.getVersion() != null && "0.6".equals(ds.getVersion())) {
                 throwException(tr("Missing attribute ''version'' on OSM primitive with ID {0}.", Long.toString(current.getUniqueId())));
-            } else if (!current.isNew() && ds.getVersion() != null && "0.5".equals(ds.getVersion())) {
-                // default version in 0.5 files for existing primitives
-                Main.warn(tr("Normalizing value of attribute ''version'' of element {0} to {2}, API version is ''{3}''. Got {1}.", current.getUniqueId(), version, 1, "0.5"));
-                version= 1;
-            } else if (current.isNew() && ds.getVersion() != null && "0.5".equals(ds.getVersion())) {
-                // default version in 0.5 files for new primitives, no warning necessary. This is (was) legal in API 0.5
-                version= 0;
             }
         }