mysql password update problem

Dear,

on a master-slave stack (everything debian 10), we have got an issue on mysql password update.
Basically what we see is that the password of the mysql database is updated not when the customer update the mysql user password, but when it updates the database itself.
Moreover, the password is updated after every modification of the database, not only if the password change.

Is that a normal behaviour or some bug exist?
To me looks strange that the password is updated all the time.
ty