Index: logback/logback-classic/src/main/java/org/slf4j/impl/LogbackMDCAdapter.java
===================================================================
--- logback/logback-classic/src/main/java/org/slf4j/impl/LogbackMDCAdapter.java	(revision 1677)
+++ logback/logback-classic/src/main/java/org/slf4j/impl/LogbackMDCAdapter.java	(working copy)
@@ -24,7 +24,15 @@
  */
 public class LogbackMDCAdapter implements MDCAdapter {
 
-  private final InheritableThreadLocal<HashMap<String, String>> inheritableThreadLocal = new InheritableThreadLocal<HashMap<String, String>>();
+  private final InheritableThreadLocal<HashMap<String, String>> inheritableThreadLocal = new InheritableThreadLocal<HashMap<String, String>>() {
+    public final HashMap<String, String> childValue(HashMap<String, String> parentValue) {
+      if(parentValue != null) {
+        return new HashMap<String, String>(parentValue);
+      } else {
+        return null;
+      }
+    }
+  };
 
   LogbackMDCAdapter() {
   }
@@ -38,12 +46,6 @@
    * If the current thread does not have a context map it is created as a side
    * effect of this call.
    * 
-   * <p>
-   * Each time a value is added, a new instance of the map is created. This is
-   * to be certain that the serialization process will operate on the updated
-   * map and not send a reference to the old map, thus not allowing the remote
-   * logback component to see the latest changes.
-   * 
    * @throws IllegalArgumentException
    *           in case the "key" parameter is null
    */
@@ -52,15 +54,14 @@
       throw new IllegalArgumentException("key cannot be null");
     }
 
-    HashMap<String, String> oldMap = inheritableThreadLocal.get();
+    HashMap<String, String> hashMap = inheritableThreadLocal.get();
 
-    HashMap<String, String> newMap = new HashMap<String, String>();
-    if (oldMap != null) {
-      newMap.putAll(oldMap);
+    if (hashMap == null) {
+      hashMap=new HashMap<String, String>()
     }
-    // the newMap replaces the old one for serialisation's sake
-    inheritableThreadLocal.set(newMap);
-    newMap.put(key, val);
+
+    inheritableThreadLocal.set(hashMap);
+    hashMap.put(key, val);
   }
 
   /**
@@ -81,23 +82,13 @@
 
   /**
    * Remove the the context identified by the <code>key</code> parameter.
-   * 
-   * <p>
-   * Each time a value is removed, a new instance of the map is created. This is
-   * to be certain that the serialization process will operate on the updated
-   * map and not send a reference to the old map, thus not allowing the remote
-   * logback component to see the latest changes.
    */
   public void remove(String key) {
-    HashMap<String, String> oldMap = inheritableThreadLocal.get();
+    HashMap<String, String> hashMap = inheritableThreadLocal.get();
 
-    HashMap<String, String> newMap = new HashMap<String, String>();
-    if (oldMap != null) {
-      newMap.putAll(oldMap);
+    if (hashMap != null) {
+      hashMap.remove(key);
     }
-    // the newMap replaces the old one for serialisation's sake
-    inheritableThreadLocal.set(newMap);
-    newMap.remove(key);
   }
 
   /**
@@ -113,11 +104,17 @@
   }
 
   /**
-   * Get the current thread's MDC as a map. This method is intended to be used
+   * Get a copy of the current thread's MDC as a map. This method is intended to be used
    * internally.
    */
   public Map<String, String> getPropertyMap() {
-    return inheritableThreadLocal.get();
+    HashMap<String, String> hashMap = inheritableThreadLocal.get();
+    
+    if(hashMap != null) {
+      return new HashMap<String, String>(hashMap);
+    } else {
+      return null;
+    }
   }
 
   /**