Altering button title it becomes inactive The override function I use in my bootstrap sub-theme template.php:

function subtheme_form_titles_node_form_alter(&amp;$form, &amp;$form_state) {
  $form['actions']['submit'] = array(
    '#type' =&gt; 'submit',
    '#value' =&gt; t('Activate'),   
  );
}


I use this, so I could replace a default 'Save' title of the button to 'Activate'. Funny thing is that it does replace the button title, but then when using the form and trying to save it by pressing 'Activate', nothing happens, the page just refresh, but content doesn't get created.

Also for some reason it change button class from btn-primary to btn-default. This shouldn't be happening. I just want to replace button text and keep default btn-primary class.
Your mistake is this line:

$form['actions']['submit'] = array(


It replaces original button with your own brand new array. Nothing in it, except what you put there. Original node form have submit function connected directly to a button, but you destroyed that with this line. 

Instead of deleting original array and creating new one, consider simply altering values you need altered, like:

$form['actions']['submit']['#value'] = t('Activate');