Magento – Attribute is not loaded on Product_List and Layered Navigation

I have a development system, here is everything working as expected. And I have a staging system, here the attribute is not loaded. It feels like, the sytem don't know, that the attribute doesn't exist in the store/attribute_set/…?

I have an attribute artist_id and this attribute is not loaded.

The collections are initialized with the attribute:

if (!is_null($this->_productCollection)) {
    return $this->_productCollection;
}
$collection = parent::_getProductCollection();
$collection->addAttributeToSelect('artist_id');

I checked wether the attribute is in the collection and it is:

[_selectAttributes:protected] => Array
    (
        [name] => 71
        [short_description] => 73
        [price] => 75
        [special_price] => 76
        [special_from_date] => 77
        [special_to_date] => 78
        [small_image] => 86
        [thumbnail] => 87
        [news_from_date] => 93
        [news_to_date] => 94
        [status] => 96
        [url_key] => 97
        [required_options] => 110
        [image_label] => 112
        [small_image_label] => 113
        [thumbnail_label] => 114
        [msrp_enabled] => 118
        [msrp_display_actual_price_type] => 119
        [msrp] => 120
        [tax_class_id] => 122
        [price_type] => 124
        [weight_type] => 126
        [price_view] => 127
        [shipment_type] => 128
        [links_purchased_separately] => 129
        [links_exist] => 132
        [artist_id] => 146
    )

But when I try to get $_product->getArtistId() there is no id.

Debugging on this system is really hard. I tried to find the part where the query is built but didn't find it yet.

UPDATE: Flat tables are OFF.

And now the bad part:
A little

<?php $_product->load($_product->getId()); ?>

in the foreach of the product/list.phtml fixes the problem 😉

To be honest: I think I broke something in the database while changing settings directy in the tables.

Is there any connection between attributes and stores?
Any ideas on this problem?