text formats - not allowed tags are saved anyway
Were not the tags supposed to be deleted by drupal?


No, the mantra in Drupal is "save the raw string, sanitise on output".

What you're seeing is the filter system working as designed.

As you mentioned in the comments, the Sanitizable (formatted text) module does exactly what you're looking for.


  The Sanitize module allows administrators to configure a text format to be applied to formatted text before storage. This is useful to ensure clean and valid data in the database.