[BUG] $URL keyword is not updated on 'svn switch'

I did an 'svn switch' to change between trunk and a release branch of clang, and the built binary still reported it was built on trunk. It uses $URL to determine this:

I did an 'svn switch' from clang trunk to the 2.8 branch, and the $URL property was not updated on Version.cpp:

~/src/llvm/tools/clang/lib/Basic $ grep '\$URL' Version.cpp
  static const char URL[] = "$URL: http://llvm.org/svn/llvm-project/cfe/trunk/lib/Basic/Version.cpp $";

~/src/llvm/tools/clang/lib/Basic $ svn info Version.cpp
Path: Version.cpp
Name: Version.cpp
URL: http://llvm.org/svn/llvm-project/cfe/branches/release_28/lib/Basic/Version.cpp
Repository Root: http://llvm.org/svn/llvm-project
Repository UUID: 91177308-0d34-0410-b5e6-96231b3b80d8
Revision: 114256
Node Kind: file
Schedule: normal
Last Changed Author: ddunbar
Last Changed Rev: 103192
Last Changed Date: 2010-05-06 11:39:38 -0700 (Thu, 06 May 2010)
Text Last Updated: 2010-05-30 17:21:25 -0700 (Sun, 30 May 2010)
Checksum: 2bae87644b9b641237ed3724456d938b

~/src/llvm/tools/clang/lib/Basic $ svn pl Version.cpp
Properties on 'Version.cpp':
  svn:keywords

~/src/llvm/tools/clang/lib/Basic $ svn pg svn:keywords Version.cpp
URL

~/src/llvm/tools/clang/lib/Basic $ rm Version.cpp

~/src/llvm/tools/clang/lib/Basic $ svn update
Restored 'Version.cpp'
At revision 114268.

~/src/llvm/tools/clang/lib/Basic $ grep '\$URL' Version.cpp
  static const char URL[] = "$URL: http://llvm.org/svn/llvm-project/cfe/branches/release_28/lib/Basic/Version.cpp $";
Received on 2010-09-18 21:21:53 CEST