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		if (!STRICMP(argv[0], "merge")) {
			argv++, argc--;
			try {
				const char* dest = argv[0];
				argv++, argc--;
				root_writer_t::instance()->copy(dest, argc, argv);
			}
...
			return 0;

Index: besch/writer/root_writer.cc
===================================================================
--- besch/writer/root_writer.cc	(revision 3397)
+++ besch/writer/root_writer.cc	(working copy)
@@ -301,7 +301,11 @@
 		} else {
 			find.search(argv[i], "pak");
 			for (searchfolder_t::const_iterator i = find.begin(), end = find.end(); i != end; ++i) {
-				any |= do_copy(outfp, root, *i);
+				if (strcmp(*i, name) != 0) {
+					any |= do_copy(outfp, root, *i);
+				} else {
+					printf("WARNING: skipping reading from output file\n");
+				}
 			}
 		}

Executing command: lift symbol.BigLogo.pak
Merging: makeobj QUIET merge GUI.128.pak *.pak
writing file GUI.128.pak
   copying file cursor.Mouse.pak
   copying file misc.Construction.pak
   copying file cursor.Marked.pak
   copying file cursor.GeneralTools.pak
   copying file symbol.Builder.pak
   copying file cursor.Builder.pak
WARNING: skipping reading from output file
My folders:  **none**

simutrans@hedwig ~ $ grep "WARNING: skipping reading from output file" /home/simutrans/PAK/PAK128/info.txt | wc -l
31