Instructions:

cd BitchX/source
patch < /path/to/75p3-format.patch

It should apply cleanly.  Then recompile bx and restart your client.

--- parse.c.orig	Fri Feb 26 11:01:55 1999
+++ parse.c	Mon Jul  3 05:17:14 2000
@@ -1030,7 +1030,7 @@
 				bitchsay("Press Ctrl-K to join %s (%s)", invite_channel, ArgList[2]);
 			else
 				bitchsay("Press Ctrl-K to join %s", invite_channel);
-			logmsg(LOG_INVITE, from, 0, invite_channel);
+			logmsg(LOG_INVITE, from, 0, "%s", invite_channel);
 		}
 		if (!(chan = lookup_channel(invite_channel, from_server, 0)))
 			if ((w_chan = check_whowas_chan_buffer(invite_channel, 0)))
@@ -1097,7 +1097,7 @@
 			fudge_nickname(from_server);
 		if (get_int_var(AUTO_RECONNECT_VAR))
 			servercmd (NULL, sc, empty_string, NULL);
-		logmsg(LOG_KILL, from, 0, ArgList[1]?ArgList[1]:"(No Reason)");
+		logmsg(LOG_KILL, from, 0, "%s", ArgList[1]?ArgList[1]:"(No Reason)");
 	}
 	update_all_status(current_window, NULL, 0);
 }