Index: trunk/src/org/openstreetmap/josm/data/osm/AbstractPrimitive.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/osm/AbstractPrimitive.java	(revision 11434)
+++ trunk/src/org/openstreetmap/josm/data/osm/AbstractPrimitive.java	(revision 11435)
@@ -538,5 +538,5 @@
     public void put(String key, String value) {
         Map<String, String> originalKeys = getKeys();
-        if (key == null || Utils.strip(key).isEmpty())
+        if (key == null || Utils.isStripEmpty(key))
             return;
         else if (value == null) {
Index: trunk/src/org/openstreetmap/josm/gui/history/VersionInfoPanel.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/history/VersionInfoPanel.java	(revision 11434)
+++ trunk/src/org/openstreetmap/josm/gui/history/VersionInfoPanel.java	(revision 11435)
@@ -274,5 +274,5 @@
         // Update text, hide prefixing label if empty
         if (label != null) {
-            label.setVisible(text != null && !Utils.strip(text).isEmpty());
+            label.setVisible(text != null && !Utils.isStripEmpty(text));
         }
         textArea.setText(text);
Index: trunk/src/org/openstreetmap/josm/gui/preferences/SourceEditor.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/preferences/SourceEditor.java	(revision 11434)
+++ trunk/src/org/openstreetmap/josm/gui/preferences/SourceEditor.java	(revision 11435)
@@ -965,5 +965,5 @@
 
         private void updateOkButtonState() {
-            buttons.get(0).setEnabled(!Utils.strip(tfURL.getText()).isEmpty());
+            buttons.get(0).setEnabled(!Utils.isStripEmpty(tfURL.getText()));
         }
 
Index: trunk/src/org/openstreetmap/josm/io/OsmReader.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/OsmReader.java	(revision 11434)
+++ trunk/src/org/openstreetmap/josm/io/OsmReader.java	(revision 11435)
@@ -25,4 +25,5 @@
 import org.openstreetmap.josm.data.DataSource;
 import org.openstreetmap.josm.data.coor.LatLon;
+import org.openstreetmap.josm.data.osm.AbstractPrimitive;
 import org.openstreetmap.josm.data.osm.Changeset;
 import org.openstreetmap.josm.data.osm.DataSet;
@@ -41,4 +42,5 @@
 import org.openstreetmap.josm.gui.progress.ProgressMonitor;
 import org.openstreetmap.josm.tools.CheckParameterUtil;
+import org.openstreetmap.josm.tools.Utils;
 import org.openstreetmap.josm.tools.date.DateUtils;
 
@@ -377,4 +379,8 @@
         if (key == null || value == null) {
             throwException(tr("Missing key or value attribute in tag."));
+        } else if (Utils.isStripEmpty(key) && t instanceof AbstractPrimitive) {
+            // #14199: Empty keys as ignored by AbstractPrimitive#put, but it causes problems to fix existing data
+            // Drop the tag on import, but flag the primitive as modified
+            ((AbstractPrimitive) t).setModified(true);
         } else {
             t.put(key.intern(), value.intern());
Index: trunk/src/org/openstreetmap/josm/tools/Utils.java
===================================================================
--- trunk/src/org/openstreetmap/josm/tools/Utils.java	(revision 11434)
+++ trunk/src/org/openstreetmap/josm/tools/Utils.java	(revision 11435)
@@ -735,4 +735,22 @@
 
     /**
+     * Determines if the given String would be empty if stripped.
+     * This is an efficient alternative to {@code strip(s).isEmpty()} that avoids to create useless String object.
+     * @param str The string to test
+     * @return {@code true} if the stripped version of {@code s} would be empty.
+     * @since 11435
+     */
+    public static boolean isStripEmpty(String str) {
+        if (str != null) {
+            for (int i = 0; i < str.length(); i++) {
+                if (!isStrippedChar(str.charAt(i), DEFAULT_STRIP)) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    /**
      * An alternative to {@link String#trim()} to effectively remove all leading
      * and trailing white characters, including Unicode ones.
@@ -774,6 +792,5 @@
         boolean leadingSkipChar = true;
         while (leadingSkipChar && start < end) {
-            char c = str.charAt(start);
-            leadingSkipChar = Character.isWhitespace(c) || Character.isSpaceChar(c) || stripChar(skipChars, c);
+            leadingSkipChar = isStrippedChar(str.charAt(start), skipChars);
             if (leadingSkipChar) {
                 start++;
@@ -782,6 +799,5 @@
         boolean trailingSkipChar = true;
         while (trailingSkipChar && end > start + 1) {
-            char c = str.charAt(end - 1);
-            trailingSkipChar = Character.isWhitespace(c) || Character.isSpaceChar(c) || stripChar(skipChars, c);
+            trailingSkipChar = isStrippedChar(str.charAt(end - 1), skipChars);
             if (trailingSkipChar) {
                 end--;
@@ -790,4 +806,8 @@
 
         return str.substring(start, end);
+    }
+
+    private static boolean isStrippedChar(char c, final char ... skipChars) {
+        return Character.isWhitespace(c) || Character.isSpaceChar(c) || stripChar(skipChars, c);
     }