Setting default values in new custom fields doesn't work

I've created three new custom fields using a module loadable package by placing the text quoted at the bottom in manifest.php. The fields were created with no problems. When I look at these fields in Studio, I see the default values set as in manifest.php. But in the layout, the fields are blank with no default values. What could be the reason for the missing default values?

'custom_fields' => array(
        //DropDown
        array(
            'name' => 'billing_milestone_term_rs_c',
            'label' => 'LBL_BILLING_MILESTONE_TERM_RS_C',
            'type' => 'enum',
            'module' => 'Opportunities',
            'help' => '',
            'comment' => '',
            'ext1' => 'billing_milestone_term_list', //maps to options - specify list name
            'default_value' => 'Single', //key of entry in specified list
            'mass_update' => false, // true or false
            'required' => false, // true or false
            'reportable' => true, // true or false
            'audited' => true, // true or false
            'importable' => 'true', // 'true', 'false' or 'required'
            'duplicate_merge' => false, // true or false
        ),
        //Checkbox
        array(
            'name' => 'billing_milestone_upsert_rs_c',
            'label' => 'LBL_BILLING_MILESTONE_UPSERT_RS',
            'type' => 'bool',
            'module' => 'Opportunities',
            'default_value' => true, // true or false
            'help' => '',
            'comment' => '',
            'audited' => true, // true or false
            'mass_update' => false, // true or false
            'duplicate_merge' => false, // true or false
            'reportable' => true, // true or false
            'importable' => 'true', // 'true', 'false' or 'required'
        ),
        //Date
        array(
            'name' => 'billing_mlst_first_date_rs_c',
            'label' => 'LBL_BILLING_MLST_FIRST_DATE_RS_C',
            'type' => 'date',
            'module' => 'Opportunities',
            'default_value' => 'today',
            'help' => '',
            'comment' => '',
            'mass_update' => false, // true or false
            'required' => false, // true or false
            'reportable' => true, // true or false
            'audited' => true, // true or false
            'duplicate_merge' => false, // true or false
            'importable' => 'true', // 'true', 'false' or 'required'
        ),

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