Combining drupal_render() in theme function causes double escaping

I have a theme function that transforms a part of a form into table.

The rows look like this:

    $row[] = drupal_render($items[$key]['thumbnail']);
    $row[] = drupal_render($items[$key]['label']) . drupal_render($items[$key]['note']);
    $row[] = drupal_render($items[$key]['value']);
    $row[] = drupal_render($items[$key]['operations']) . drupal_render($items[$key]);

Note the second and last rows - they combine multiple fields into one row.
These cells will get double escaped by Twig autoescape.
The rows with only one item gets rendered just fine.

This is due to the fact that each render is marked as safe separately. But when they are put together they make up a new and unique string which is not present in SafeMarkup's static cache and therefore it's not treated as safe.

Simple solution for tables is to put the data into separate cells and use colspan.