What's the odt file and why its content wasn't updated when using lettre package

I have a letter document that I have written on 23/12/2013. Today I have copied the directory that contains the tex file along all the other files generated after compilation. I have changed the tex file and I have noticed that LaTex keep the original date (23/12/2013) even though I have used the command \today.

When I looked to log file I found that LaTeX read the date from the odt file and the contents of this file wasn't updated with the correct date.

\expandafter\def\csname origdate1\endcsname{le 23/12/2013}


I have also this warning:

Package lettre Warning: Mode origdate'.


What's the cause of my problem?

This is the expected behavior. If origdate option is selected, and the file .odt exists, lettre uses the date from this file. Otherwise it stores the current date there.
If you do not need the feature, just delete .odt file or the option origdate`.