I am developing my first SS3 website and implemented a GridField. It was pretty tough, since this new concept isn't documented well in my opinion.

Anyway, I think it is working now, but why is there always a dropdown showing the current page? I didn't tell SS to show this field and I don't know how to remove it.

For example …
http://doc.silverstripe.org//src/framework_3.0/docs/en/tutorials/_images/tutorial5_addNew.jpg
In chapter 5 of the SS tutorial the page "Developer Toolbar" has a GridField attached and when I edit an item at the bottom it shows the field "Project". Without any purpose. I can't even edit/change it.

Is this a bug?

This is because the default getCMSFields() method includes fields for every relation on the DataObject, including the one that GridField manages. You can remove it by defining a getCMSFields() method on your DataObject that looks something like:

	public function getCMSFields() {
		$fields = parent::getCMSFields();
		$fields->removeByName('ProjectID');
		return $fields;
	}

Cool. Thanks for your reply. Works!