I'm not sure what was happening here:

If ALLOW_DISABLED_PLAYER_INPUT is true (only ScreenTitleMenu), then
ScreenSelect::Input doesn't do JoinInput ("the player will be joined
and the user will still be on the title menu").  However,
ScreenSelectMaster::MenuStart does the JoinInput anyway, so this still
happens.

If we want to have main menu options that don't load a screen, this
code path should be refactored a bit, to ask the derived class whether
the selection should also join.  As is, it's just making the JoinInput
path complicated.

stepmania/src/ScreenSelect.cpp

@@ -142,12 +142,7 @@ void ScreenSelect::Input( const InputEventPlus &input )
 	if( input.MenuI == MENU_BUTTON_COIN && input.type == IET_FIRST_PRESS )
 		this->UpdateSelectableChoices();
 
-	// HACK: Don't process JoinInput on the TitleMenu.  Otherwise, if the user presses start
+	if( input.MenuI == MENU_BUTTON_START && Screen::JoinInput(input.pn) )
-	// on a choice that doesn't move to a new screen, the player will be joined and the
-	// user will still be on the title menu.
-	bool bAllowJoinInput = !ALLOW_DISABLED_PLAYER_INPUT;
-
-	if( bAllowJoinInput && input.MenuI == MENU_BUTTON_START && Screen::JoinInput(input.pn) )
 	{
 		if( input.type == IET_FIRST_PRESS )
 			this->UpdateSelectableChoices();

stepmania/src/ScreenSelectMaster.cpp

@@ -714,10 +714,6 @@ void ScreenSelectMaster::MenuStart( const InputEventPlus &input )
 		return;
 	PlayerNumber pn = input.pn;
 	
-	// If the player isn't already joined, try to join them.
-	// Allow a player to join even if input is locked or someone has already already chosen.
-	Screen::JoinInput( pn );
-
 	if( m_fLockInputSecs > 0 )
 		return;
 	if( m_bChosen[pn] )