http://bugs.winehq.org/show_bug.cgi?id=13945
--- Comment #1 from Kai Blin kai.blin@gmail.com 2008-07-28 13:04:42 --- Sorry, I seem to have missed this bug for some reason.
Your solution will break a couple of other applications that expect Negotiate to work if the Negotiate provider is loaded.
I'm not convinced that svn actually needs Negotiate for anything, could you provide a +secur32 trace?