title: Core-data raises "The file has been changed by another application"
body: <p>When changing data in my core-data application, a error message comes up: </p>
  
  <blockquote>
    <p>The document “xyz.sqlite” could not be saved. The file has been
    changed by another application.</p>
  </blockquote>
  
  <p>In fact, there is no other application that has changed data. I observed in addition, that the undo management is not working well then.</p>
  
  <p>Probably, I should not use more than one (unique?) Arraycontroller bound to the managedObjectContext for one entity ? </p>
  
  <p>In my app, I use a classical master-detail relationship setup with 2 controllers for each entity - and 2 table views to display the data. </p>
  
  <p>But, in addition I want to present a list of all details, where I can change the master. Therefore, I am using another Array controller bound to the same managedObjectContext. This one does not have a content set to the master, so it will have all detail objects. Using this approach makes it easy to manage the relationship in the associated tableview (by simply binding "selected Object" to the relationship of the detail) - but it seems to impact the app.</p>
  
  <p>Does anybody else face this issue ? Any idea is welcome !</p>