2 files changed, 12 insertions, 2 deletions
diff --git a/core/java/android/app/SharedPreferencesImpl.java b/core/java/android/app/SharedPreferencesImpl.java
index 201d7b2..86fd7b9 100644
--- a/core/java/android/app/SharedPreferencesImpl.java
+++ b/core/java/android/app/SharedPreferencesImpl.java
@@ -312,7 +312,8 @@ final class SharedPreferencesImpl implements SharedPreferences {
         }
         public Editor putStringSet(String key, Set<String> values) {
             synchronized (this) {
-                mModified.put(key, values);
+                mModified.put(key,
+                        (values == null) ? null : new HashSet<String>(values));
                 return this;
             }
         }
diff --git a/core/java/android/content/SharedPreferences.java b/core/java/android/content/SharedPreferences.java
index bdc38d6..da5480e 100644
--- a/core/java/android/content/SharedPreferences.java
+++ b/core/java/android/content/SharedPreferences.java
@@ -25,7 +25,8 @@ import java.util.Set;
  * there is a single instance of this class that all clients share.
  * Modifications to the preferences must go through an {@link Editor} object
  * to ensure the preference values remain in a consistent state and control
- * when they are committed to storage.
+ * when they are committed to storage.  Objects that are returned from the
+ * various <code>get</code> methods must be treated as immutable by the application.
  *
  * <p><em>Note: currently this class does not support use across multiple
  * processes.  This will be added later.</em>
@@ -226,6 +227,10 @@ public interface SharedPreferences {
     /**
      * Retrieve all values from the preferences.
      *
+     * <p>Note that you <em>must not</em> modify the collection returned
+     * by this method, or alter any of its contents.  The consistency of your
+     * stored data is not guaranteed if you do.
+     *
      * @return Returns a map containing a list of pairs key/value representing
      * the preferences.
      *
@@ -250,6 +255,10 @@ public interface SharedPreferences {
     /**
      * Retrieve a set of String values from the preferences.
      * 
+     * <p>Note that you <em>must not</em> modify the set instance returned
+     * by this call.  The consistency of the stored data is not guaranteed
+     * if you do, nor is your ability to modify the instance at all.
+     *
      * @param key The name of the preference to retrieve.
      * @param defValues Values to return if this preference does not exist.
      *