HEAD svnserve broken with 1.6 client

The HEAD svnserve crashes when used with a 1.6 client:

svnadmin create repo
printf "[global]\nanon-access=write\n" > repo/conf/svnserve.conf
svn mkdir -mm file://`pwd`/repo/A
svnserve -dr. # 1.7 server
svn cp -mm svn://localhost/repo/A svn://localhost/repo/B # 1.6 client

The server crashes in vparse_tuple called from get_mergeinfo.

-- 
Philip