Working copy path [...] does not exist in repository

Hi all.

The usual apologies if I'm doing something stupid or the like.

I'm running into an issue when attempting to perform a merge with
Subversion, where I'm getting an error along the lines of "Working copy
path [...] does not exist in repository". This is on a Sourceforge
project, so should be easy to reproduce:

$ $ svn --version
svn, version 1.5.1 (r32289)
   compiled Jul 24 2008, 20:58:29
[ ... ]
$ svn co https://fuse-emulator.svn.sourceforge.net/svnroot/fuse-emulator/trunk/fuse
[ ... ]
Checked out revision 3939.
$ cd fuse
$ svn merge https://fuse-emulator.svn.sourceforge.net/svnroot/fuse-emulator/branches/wii-20080828/fuse
svn: Working copy path 'ide' does not exist in repository

The path 'ide' definitely does exist in both branches, although it was
created after the branch was taken.

Some questions:

1) Am I doing something stupid?
2) If not, is this a symptom of issue #3067 (subtrees that don't exist at
the start or end of a merge range shouldn't break the merge), or something
else?
3) Is there any way to work around this issue and to get the changes
from /branches/wii-20080828 back onto /trunk? (I can build my own
binaries if necessary, but I'd rather not if it can be avoided :-) )

Thanks for any pointers,

Phil

-- 
  Philip Kendall <philip_at_shadowmagic.org.uk>
  http://www.shadowmagic.org.uk/