服务器重新做了，但那个400 bad request的错误还是存在，再次Google找到2个相关讨论
when I try to check out a subversion repository
> svn co http://scm.sipfoundry.org/rep/project/main project
I get an error like:
svn: REPORT request failed on '/rep/project/!svn/vcc/default'
svn: REPORT of '/rep/project/!svn/vcc/default': 400 Bad Request (http://scm.sipfoundry.org)
You are behind a web proxy that is not passing the WebDAV methods that subversion uses. You can work around the problem by using SSL to hide what you're doing from the proxy:
> svn co https://scm.sipfoundry.org/rep/project/main project
很明显解决办法与我的方法相同，但是对于原因的解释我并不认可。还有另一个资料:
I sniffed the traffic between the client and server and the error
seems to occur after authentication occurs, during the following
exchange. Note the missing closing > in both hunks of XML. The same
behavior is repeatable and occurs with both clients.
The trace:
...
REPORT /LNSS/!svn/vcc/default HTTP/1.1
Host: svn.lifetouch.net
User-Agent: SVN/1.3.2 (r19776) neon/0.25.5
Connection: TE
TE: trailers
Content-Length: 236
Content-Type: text/xml
Accept-Encoding: gzip
Accept-Encoding: gzip
Authorization: Basic xxx=
Date: Tue, 05 Sep 2006 21:32:00 GMT
Server: Apache/2.0.55 (Win32) mod_auth_sspi/1.0.3 SVN/1.3.0 DAV/2
Content-Length: 344
Connection: close
Content-Type: text/html; charset=iso-8859-1
这个作者对svn的请求做了抓包，很简单的就跟踪到了结果: 发送的update请求不完整，漏掉了一个">"符号。怀疑是新版svn客户端的bug.
期待svn的更新吧。