Why does my version number keep changing?

[Extreme Unction]

On the main menu, where you pick "Single Player", "Multiplayer", "Tutorials", etc. Down at the bottom left corner. It says:

v5.1 (XXXX)

Where the "XXXX" is four letters.

I was putzing around with the game, continually starting and resigning and restarting new games, just to see some of the different religious and cultural decisions available for different cultures and religions. And I noticed that the "XXXX" letters were changing. I started one game and it said "v5.1 (SILT)". When I resigned that game and came back to the main menu, it said "v5.1 (RILT)". And I distinctly recall it saying "v5.1 (BJLT) a few days ago.

What's up with that?

 

[jdrou]

Any time you resign from the game without quitting to the desktop the checksum will change.
This is to force people that get disconnected from a MP game to quit completely before attempting to rejoin (since you can't join MP unless all checksums match).