Simply the explanation is that in 0.12 version the extension files are "savegame.s0n" and in 0.13 version are "savegame.S0n".
I´ve discovered this feature with resco explorer. The wince explorer doesn´t shows extensions of files.
Forgive me my poor spanglish.
![Smile :-)](./images/smilies/icon_smile.gif)
(Thank you fingolin).
Edited by myself, I think this way may be more clearly than before.