Custom field rendering in modern list views

So, I'm sure someone else has already spotted this, but if I create a new page with the modern UI and add the Lists (preview) webpart and select my list with the calculated column in it, my button renders!!! If inspect the element the URL is correct, however if I click the button itself it takes me to the item form rather than the URL defined in the HTML. Bizarre and inconsistent behaviour. 

Anyone else seeing this and even better, explain this???