I think there's a bug in richtexteditor/dialogs/browsedialogbase.xml, in the file-list context menu.

Lines 384+:

<panel jsml-base="rtemenuitem" htmlcode="@COPY" src="{folder}images/copy.png">
  <attach name="updateitem" arguments="jevent,item">
    self._currentitem=item;
    var s=option.dialogcontrol._selectedstorage;
    if(item.IsFolder)self.set_disabled(!s.AllowMoveFolder);
    else self.set_disabled(!s.AllowMoveFile);
  </attach>
  <attach name="click">

   if(self._disabled)return;

   option.dialogcontrol.processmenucommand("copy",self._currentitem);
  </attach>
</panel>

I think they should be AllowCopyFolder and AllowCopyFile.