While changing a password, whether for yourself or performing a password reset for others, the password field contains a masked value. We are deleting it and adding a new value, but this is functionality that did not occur in 12.6, as the password field defaulted to blank.
In Identity Manager there is no out of the box option for configuring the password field to be blank. Most likely you had customized the screen configuration to clear the field.
In the task's profile screen there is an option to add initialization java script. Most likely you had some custom .js there for the password field.
To get to the profile screen configuration for the above customization, in the user environment go to ....
Roles and Tasks
Modify Admin Task
Search for and select your task (for example, Change My Password)
Click the 'Tabs' tab
Click to edit Profile tab in the Screen field click Browse
Select the screen and click Edit
On the Password field click to Edit the field properties
Save the changes (apply, okay, select, submit...)