Trouble with password persistence using 2.0.5

Help !
I'm in trouble : I'm using Jigsaw 2.0.5, classes 19/10/2000, jdk 1.2 under NT4 sp 5.
I've added in my site the change password frame 
for people been able to change  their password ( I'm using Basic authentification ).

What happen is : a user change his password; it works fine with the new password.
Next day, same user try to connect again : new password don't works and he needs to use old one.

I have 3 to 5 users having that problem, on a total of 180 approximatively ( others one might not change their password ).

I have no clue about what's the cause.

A user told me that he tried to access a forbidden part of the serveur ( authorization been managed per group assigned to directory )
and after that he was not able to use again it's password.
I tried, it worked without problem.

Another clue is that this morning, my <real name>.db file has been updated; nobody used the JigAdmin tool at that time.

I'm really in the fog here; could someone of the Jigsaw team have a look at that ?

Thanks - 
Jacques Brax