diff -r a64e5904bbb7 projectapi/src/org/netbeans/modules/projectapi/SimpleFileOwnerQueryImplementation.java
--- a/projectapi/src/org/netbeans/modules/projectapi/SimpleFileOwnerQueryImplementation.java	Mon Jun 16 19:32:53 2008 +0200
+++ b/projectapi/src/org/netbeans/modules/projectapi/SimpleFileOwnerQueryImplementation.java	Fri Jun 20 16:09:14 2008 +0200
@@ -54,6 +54,9 @@ import java.util.Map;
 import java.util.Map;
 import java.util.Set;
 import java.util.WeakHashMap;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import java.util.prefs.Preferences;
 import org.netbeans.api.project.Project;
 import org.netbeans.api.project.ProjectManager;
 import org.netbeans.spi.project.FileOwnerQueryImplementation;
@@ -61,6 +64,7 @@ import org.openide.filesystems.FileObjec
 import org.openide.filesystems.FileObject;
 import org.openide.filesystems.FileStateInvalidException;
 import org.openide.filesystems.URLMapper;
+import org.openide.util.NbPreferences;
 import org.openide.util.Utilities;
 import org.openide.util.WeakSet;
 
@@ -172,8 +176,26 @@ public class SimpleFileOwnerQueryImpleme
     private static final Map<FileObject,Collection<URI>> project2External =
         Collections.synchronizedMap(new WeakHashMap<FileObject,Collection<URI>>());
     
+    static {
+        try {
+            Preferences p = NbPreferences.forModule(SimpleFileOwnerQueryImplementation.class).node("externalOwners");
+            for (String name : p.keys()) {
+                URL u = new URL(p.get(name, null));
+                URI i = new URI(name);
+                externalOwners.put(i, new WeakReference<FileObject>(URLMapper.findFileObject(u)));
+            }
+        } catch (Exception ex) {
+            Logger.getLogger(SimpleFileOwnerQueryImplementation.class.getName()).log(Level.WARNING, null, ex);
+        }
+    }
+    
     /** @see FileOwnerQuery#reset */
     public static void reset() {
+        try {
+            NbPreferences.forModule(SimpleFileOwnerQueryImplementation.class).node("externalOwners").removeNode();
+        } catch (Exception ex) {
+            Logger.getLogger(SimpleFileOwnerQueryImplementation.class.getName()).log(Level.WARNING, null, ex);
+        }
         externalOwners.clear();
     }
     
@@ -194,7 +216,13 @@ public class SimpleFileOwnerQueryImpleme
     public static void markExternalOwnerTransient(URI root, Project owner) {
         externalRootsIncludeNonFolders |= !root.getPath().endsWith("/");
         if (owner != null) {
-            externalOwners.put(root, new WeakReference<FileObject>(owner.getProjectDirectory()));            
+            FileObject fo = owner.getProjectDirectory();
+            externalOwners.put(root, new WeakReference<FileObject>(fo));
+            try {
+                NbPreferences.forModule(SimpleFileOwnerQueryImplementation.class).node("externalOwners").put(root.toString(), fo.getURL().toExternalForm());
+            } catch (Exception ex) {
+                Logger.getLogger(SimpleFileOwnerQueryImplementation.class.getName()).log(Level.WARNING, null, ex);
+            }
             synchronized (project2External) {
                 FileObject prjDir = owner.getProjectDirectory();
                 Collection<URI> roots = project2External.get (prjDir);