When cache is enabled, the default message is the name of the variable stores it

I raised this issue as a seperate one, taken from here

This is easily solved by changing in hide_submit_admin.inc

instead:

 $form['fieldset_message']['hide_submit_message'] = array(
    '#type' => 'textarea',
    '#title' => t('Default Message'),
    '#rows' => 2,
    '#default_value' => variable_get('hide_submit_message', HIDE_SUBMIT_DEFAULT_MESSAGE ),
  );

Just hard-code the default message,

 $form['fieldset_message']['hide_submit_message'] = array(
    '#type' => 'textarea',
    '#title' => t('Default Message'),
    '#rows' => 2,
    '#default_value' => variable_get('hide_submit_message', t('Please wait...')),
  );

Usually I don't like hard-coding constants, but in this case it is bearable
I can see that this method is common in many drupal modules, including core modules

I'll commit this soon