diff --git a/wise-webapp/src/main/java/com/wisemapping/dao/UserManagerImpl.java b/wise-webapp/src/main/java/com/wisemapping/dao/UserManagerImpl.java
index 663fe9d2..bea65dcd 100644
--- a/wise-webapp/src/main/java/com/wisemapping/dao/UserManagerImpl.java
+++ b/wise-webapp/src/main/java/com/wisemapping/dao/UserManagerImpl.java
@@ -115,6 +115,7 @@ public class UserManagerImpl
             Collaboration newCollab = new Collaboration();
             newCollab.setRoleId(oldCollab.getRole().ordinal());
             newCollab.setMindMap(oldCollab.getMindMap());
+            oldCollab.getMindMap().removedCollaboration(oldCollab);
             newCollab.setCollaborator(user);
             user.addCollaboration(newCollab);
             newCollabs.add(newCollab);
@@ -124,7 +125,6 @@ public class UserManagerImpl
         final HibernateTemplate template = getHibernateTemplate();
         collaborations.forEach(c -> template.delete(c));
         template.delete(collaborator);
-        template.flush();
 
         // Save all new...
         this.createUser(user);
diff --git a/wise-webapp/src/main/java/com/wisemapping/model/Collaboration.java b/wise-webapp/src/main/java/com/wisemapping/model/Collaboration.java
index 0ab3ce73..7446b6f5 100644
--- a/wise-webapp/src/main/java/com/wisemapping/model/Collaboration.java
+++ b/wise-webapp/src/main/java/com/wisemapping/model/Collaboration.java
@@ -21,6 +21,7 @@ package com.wisemapping.model;
 
 import org.hibernate.annotations.Fetch;
 import org.hibernate.annotations.FetchMode;
+import org.jetbrains.annotations.Nullable;
 
 import javax.persistence.*;
 import javax.validation.constraints.NotNull;
@@ -46,7 +47,7 @@ public class Collaboration implements Serializable {
     private Collaborator collaborator;
 
     @ManyToOne(cascade = CascadeType.ALL)
-    @JoinColumn(name = "properties_id", nullable = false, unique = true)
+    @JoinColumn(name = "properties_id", nullable = true, unique = true)
     private CollaborationProperties collaborationProperties = new CollaborationProperties();
 
     public Collaboration() {
@@ -103,12 +104,13 @@ public class Collaboration implements Serializable {
         this.collaborator = collaborator;
     }
 
-    @NotNull
+
+    @Nullable
     public CollaborationProperties getCollaborationProperties() {
         return this.collaborationProperties;
     }
 
-    public void setCollaborationProperties(@NotNull CollaborationProperties collaborationProperties) {
+    public void setCollaborationProperties(@Nullable CollaborationProperties collaborationProperties) {
         this.collaborationProperties = collaborationProperties;
     }