svn lost track of a subdirectory

I have a checkout in . and part of the checkout is a directory
./data. I've been using this checkout for a while, updating and
committing not only in the root, but also in subtrees.

As of this morning, updates do no longer work, I get the following
instead:

  piper:~/phd> svn up data
  svn: Failed to add directory 'data': object of the same name already exists
  
  piper:~/phd> svn info . data #[1,408]
  Path: .
  URL: svn+ssh://svn.madduck.net/srv/svn/svn.madduck.net/phd
  Repository Root: svn+ssh://svn.madduck.net/srv/svn/svn.madduck.net
  Repository UUID: d3a7e407-1618-0410-b472-f1f387cadc13
  Revision: 483
  Node Kind: directory
  Schedule: normal
  Last Changed Author: madduck
  Last Changed Rev: 393
  Last Changed Date: 2007-01-22 17:06:19 +0100 (Mon, 22 Jan 2007)

  Path: data
  URL: svn+ssh://svn.madduck.net/srv/svn/svn.madduck.net/phd/data
  Repository Root: svn+ssh://svn.madduck.net/srv/svn/svn.madduck.net
  Repository UUID: d3a7e407-1618-0410-b472-f1f387cadc13
  Revision: 483
  Node Kind: directory
  Schedule: normal
  Last Changed Author: madduck
  Last Changed Rev: 429
  Last Changed Date: 2007-02-06 21:03:46 +0100 (Tue, 06 Feb 2007)

I note that the two directories are at the same revision, have the
same UUID and the same root. So what is SVN's problem???

I know I could move the data directory out of the way and update, then
resynchronise, but I cannot do that right now as there are
long-running processes using the directory and I thus don't want to
mess with it.

There has to be way to stop SVN from barfing over it's own metadata.

Thanks for any tips.

-- 
martin;              (greetings from the heart of the sun.)
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