SSIS package loses .NET provider password even though EncryptSensitiveWithPassword is enabled

I have a new SSIS project developed in VS and intended to run on a SQL Server 2016 instance. The project has the ProtectionLevel of EncryptSensitiveWithPassword set. A package has a connection to a .Net Provider and this works in the package (both connection test and package run) after the SQL Server Authentication password is entered. However, if I later review the connection properties the password is missing. Why is the password being removed when the ProtectionLevel is set as it is?