Error when applying hunk in Diff buffer

[Marshall, Simon]

To reproduce:

C-x C-f ChangeLog RET
C-x v v
Remove a line
C-x v = SPC
Move to the *vc-diff* buffer and the change you have made, then:
C-c C-a

I get a buffer read-only error.  It looks like vc is trying to use the wrong
buffer.  For me, the *vc-diff* buffer contains:

*** ChangeLog.~1.481.~  Mon Jul 17 09:47:44 2006
--- ChangeLog   Thu Jul 20 11:59:52 2006
***************
*** 1,7 ****
  2006-07-14  Eli Zaretskii  <address@hidden>
  
        * configure.in (PKG_CHECK_MODULES): Redirect the output of
-       $PKG_CONFIG --exists "$2" to config.log.
        * configure: Regenerated.
  
  2006-07-14  Kim F. Storm  <address@hidden>
--- 1,6 ----

In GNU Emacs 22.0.50.2 (sparc-sun-solaris2.8, Motif Version 2.1.0)  of
2006-07-19 on perth X server distributor `Hummingbird Ltd.', version
11.0.100015 configured using `configure
'--prefix=/rvcarma/marshals/software/slash/usr/local'
'--with-x-toolkit=motif' 'CFLAGS=-g''