There is a bug in libproxy that lead to meld always crashing on start if Windows is configured to use proxy for all urls but some exceptions.
http://code.google.com/p/libproxy/issues/detail?id=207
Chances are that libproxy developers would apply patch, but the latest release is more than a 1 year ago.
Knowing that meld is preparing msi meld Windows installer now, I decide to inform meld and pygobjectwin32 projects about this bug.
Patch is attached on libproxy issue tracker and is quite simple.