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This is still an issue as of OpenBSD 5.6. Here is an updated patch for the latest 2.7 branch:
diff -r 88de50c1696b Modules/socketmodule.c
--- a/Modules/socketmodule.c Sun Dec 28 18:51:25 2014 +0200
+++ b/Modules/socketmodule.c Sun Dec 28 21:24:41 2014 -0500
@@ -1881,24 +1881,29 @@
 {
 int level;
 int optname;
 int res;
 char *buf;
 int buflen;
 int flag;
 
 if (PyArg_ParseTuple(args, "iii:setsockopt",
 &level, &optname, &flag)) {
 buf = (char *) &flag;
 buflen = sizeof flag;
+ /* Multi cast options take shorter arguments */
+ if (optname == IP_MULTICAST_TTL
+ || optname == IP_MULTICAST_LOOP)
+ buflen = sizeof(u_char);
+ buf = (char *) &flag;
 }
 else {
 PyErr_Clear();
 if (!PyArg_ParseTuple(args, "iis#:setsockopt",
 &level, &optname, &buf, &buflen))
 return NULL;
 }
 res = setsockopt(s->sock_fd, level, optname, (void *)buf, buflen);
 if (res < 0)
 return s->errorhandler();
 Py_INCREF(Py_None);
 return Py_None;