drupalPost

I'm using SimpleTest to test my custom CCK content type. Here is an example:

$this->drupalPost('node/1/edit', array('field_comp_addmargin[0][value]' => 0),'Save');

It actually saves the value, but for some reason it doesn't go through standard drupal handlers.. For example after I submit node_edit form it should fire nodeapi update event. In my case it not happens for some reason and because of that my custom piece of code which should be executed on nodeapi update never gets executed..