Lion Apache Subversion (SVN) ignore problem
The problem with GUI editors is that when launched from the command-line, they generally do not halt the process in the shell. That's why when editing a property, svn will create the temporary file, launch the editor, and wait for the exit signal to read and delete the temporary file contents. Because the GUI editor returns the exit signal immediately upon launching, the file will no longer be there.

Some GUI editors like TextMate and Sublime Text support a -w (wait) option from the command-line, forcing them to halt the SVN process until the file is closed. I am not aware of TextEdit supporting such an option.

You probably want to change your SVN editor to something more appropriate, like vim or nano. You can change the editor command in ~/.subversion/config