WPF DataGrid calls BeginEdit on an IEditableObject two times?

I've got a DataGrid bound to a collection of IEditableObject's.

Now when I click two times in a cell, it will be opened for editing.

Funny thing is: BeginEdit will be called two times. Sometimes for the same EditableObject, but sometimes for two different objects (especially when I use PgDn until I hit the end of the DataGrid) the correct one will be called first, then some other item from the collection, which never had been in focus before.

EndEdit is called twice, too, but always for the selected Item, not for the wrong one.

Is this a known problem? Any workarounds to get only (the right) one notification.