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 {

src/tools/keymods.cpp

@@ -91,3 +91,10 @@ bool keymods_t::handleModifier(const sf::Event& evt) {
 	}
 	return true;
 }
+
+void keymods_t::flushModifiers() {
+	alt = false;
+	ctrl = false,
+	shift = false,
+	meta = false;
+}

src/tools/keymods.hpp

@@ -26,6 +26,7 @@ public:
 	bool isLeftPressed() const;
 	bool isRightPressed() const;
 	bool handleModifier(const sf::Event& evt);
+	void flushModifiers();
 };
 
 extern keymods_t kb;