Please also consider using the svn command line for this (and/or the 
TortoiseSvn's SubWCRev utility, on Windows), as this would guarantee forward 
compatibility.

Trac users have been hitting this problem pretty consistently for the 1.4.x to 
1.5.x upgrade and now for the 1.5.x to 1.6.x upgrade. Let's avoid this for 1.7.x 
and upward.

See also issue4 and issue44 and http://trac.edgewall.org/ticket/8151.