Just as a slight note to self, but possibly useful for others running Subversion under Apache 2 on Windows (2008 in my case) behind Forefront TMG (nextgen ISA Server). The setup was working very good until I tried committing a move or a copy from my local machine. Typically things started going wrong when doing renames with ReSharper through VisualSVN in Visual Studio.You'll see errors like these:
"Server sent unexpected return value (502 Bad Gateway) in response to COPY"
Some research will quite quickly identify the problem as related to the use of a reverse proxy (Forefront in my case) and problems when using https externally and http internally. Christian Stocker suggests using a perl script to solve this problem, and Tor Håkon Haugen adds some more SSL config, but there is a much simpler solution available if your setup is much like mine. Just add this line to your httpd.conf:
RequestHeader edit Destination ^https http early