When new users are created in Stash the directory cannot be chosen. To create a user in a specific directory the directory position must be changed. Since, the directory type cannot be chosen the password field is enabled when creating a user who belongs to a delegated directory.
If you are trying to create a user and assign it to "Delegated LDAP", place your directory as the first one on the "User Directory" list. Once you manually create a user in Stash, it will be automatically assigned to your delegated LDAP directory:
User Directory List:
Manually created user when Delegated LDAP is the first one on the list: