Fix #476 directly

src/game/boe.startup.cpp

@@ -80,6 +80,9 @@ void handle_startup_button_click(eStartButton btn, eKeyMod mods) {
 		case STARTBTN_JOIN:
 			if(!party_in_memory) {
 				if(mod_contains(mods, mod_alt)) {
+					// This is a special case fix for issue #476:
+					kb.flushModifiers();
+
 					force_party = true;
 					start_new_game(true);
 				} else {