Well, I've looked through the code and confirmed (twice now) that it's impossible. Either you're not describing your problem correctly, or your save game is borked. And yes, saving in a modded version can carry along garbage if you load that save in an unmodded version.
Additionally, neither the link in the first post nor the modded version you used is official. The former is a pirated copy outside my control, and the latter is, well... modded. I'm afraid there's not much I can do to help you except to ask you to check the variable named "weekday_text_lowercase" to see if it changes to a properly named lowercase weekday name every day in the game. Beyond that, I can't be expected to support pirated or modded games. That way lies madness.
