Try to mime-insert a text file in a mail, then undo, and
repeat-complex-command. tm will kindly give you the mime encapsulation back,
but with an empty file inside. The following patch fixes it.
	BTW, this bring another question to my mind: this problem was due to
repeating the command in a non interactive fashion. What if
repeat-complex-command let us choose to repeat in a [non]interactive way ? I'm 
not sure it's worth it, but ...
1998-04-23  Didier Verna  <verna(a)inf.enst.fr>
	* tm-edit.el (mime-editor/insert-file): if nil encoding, ask the
	user which one to use. 
--- lisp/tm/tm-edit.el.orig	Thu Apr 23 14:27:28 1998
+++ lisp/tm/tm-edit.el	Thu Apr 23 14:28:17 1998
@@ -910,7 +910,7 @@
 	(setq type    (mime-prompt-for-type type)
 	      subtype (mime-prompt-for-subtype type subtype)
 	      ))
-    (if (or (interactive-p) verbose)
+    (if (or (interactive-p) verbose (null encoding))
 	(setq encoding (mime-prompt-for-encoding encoding))
       )
     (if (or (consp parameters) (stringp disposition-type))