Taxonomy not being saved - bolt cms

Question

I'm using Bolt CMS and I have this contenttype 'nl_tours' and an English version of it called 'tours'. Those two are nearly identical and both have a taxonomy: [ categories ]. It allows me to create tours correctly but for some reason the taxonomy value of nl_tours stays null in the database.

nl_tours:
    name: Rondleidingen
    singular_name: Rondleiding
    fields:
        title: 
            type: text
        slug:
            type: slug
            uses: title
        image:
            type: image
        teaser:
            type: html
            height: 150px
        body:
            type: html
            height: 300px
        length: 
            type: select
            values: [0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5]
        total price:
            type: integer
    taxonomy: [ categories ]
    record_template: tour.twig

Any idea's how this is possible?