Madan U S <madan@collab.net> found this, and I can reproduce it:
If you run 'svn mv' on a versioned file with local mods in the current working
directory, the local mods are lost. But if you run the move from one directory
level above, the mods are not lost! Attached are two scripts demonstrating
this. The first (mv-in-cwd.sh) reproduces the bug. The second
(mv-from-above.sh) shows how the bug does not happen when running from the
parent dir.
This is with Subversion 1.4.0 (trunk dev build, r17234) on Debian GNU/Linux
2.4.26-1-386. We've also reproduced it on Fedora Core 2.