Minor thing: if I understand correctly, then FillSaveGameList() fills SaveGameSlots[] which is an array of up to 50 entries; whereas ListBoxSaveGameList() fills savegameindex[] which is an array of up to 20 entries. This is not that big a deal, but the manual specifies 50, and using the latter method with more than 20 saved games causes an array out of bounds exception.
ListBox.FillSaveGameList() and ListBoxSaveGameList() are essentially the same thing, only called differently.
They both fill ListBox.SaveGameSlots AND savegameindex. And both arrays have size of 50 in the engine.
The savegameindex is declared with size 20 in the editor, though, which might be a mistake.
E: Right, forgot to tell, this was fixed in some of the 3.3.0 betas.