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.