git-svn in 1.5.4~rc2 somewhat broken?

I just tried to run "git svn fetch" on a clone of a Subversion
repository that used to work fine with 1.5.3.  After trying to fix some
things up (sorry, scrollback buffer is not deep enough), it now reports
an index mismatch:

Index mismatch: efcc3165fb64519ff1784903112d725c8682d5d2 != b3e7f07b5e4b79f682718fe6a31107d74ca35ce6

And it finally bails out with:

Last fetched revision of refs/remotes/git-svn was r45313, but we are about to fetch: r851!

This doesn't make sense because all paths (both log messages and
.git/config) refer to:

  http://llvm.org/svn/llvm-project/llvm/trunk

And this repository certainly contains revisions after r851.

With other repositories, it also peforms an index rebuild, but succeeds.