after call of g_slist_remove() the `pos` points to released area,
so dereferencing pos->data isn't acceptable.

--- irssi-0.8.10/src/irc/dcc/dcc.c.orig	2005-10-19 04:13:31.000000000 +0200
+++ irssi-0.8.10/src/irc/dcc/dcc.c	2006-05-02 22:33:11.000000000 +0200
@@ -55,11 +55,13 @@
 void dcc_unregister_type(const char *type)
 {
 	GSList *pos;
+	gpointer data;
 
 	pos = gslist_find_string(dcc_types, type);
 	if (pos != NULL) {
-                dcc_types = g_slist_remove(dcc_types, pos->data);
-		g_free(pos->data);
+		data = pos->data;
+		dcc_types = g_slist_remove(dcc_types, data);
+		g_free(data);
 	}
 }