TYPO3 Core

If I set a field in my extension table to a read only field with the following TCA definition, the formatting is gone and I only see the number of seconds.

'duration' => array (
  'exclude' => 1,
  'label' => 'LLL:EXT:my_extkey/locallang_db.xml:tx_myextkey_tablename.duration',
  'config' => array (
    'type' => 'input',
    'size' => '8',
    'max' => '8',
    'eval' => 'timesec',
    'readOnly' => 1,
  )
),

Without readonly attribute, the form field is formatted in Time:Sec. It would be really helpful, if the formatting of a field is not gone, if the field is read only.