Radiobuttons look broken after update

We got reports that the radio buttons on our form look weird and broken. Can confirm that after checking the page. Suddenly – after an auto update? – they look pretty weird:

https://i.imgur.com/CsBSkST.png

Downgrading to 3.6.9 fixes the issue.

In 3.6.9 you can find a CSS definition for the radio input field in the DOM inspector:

./wp-content/plugins/ninja-forms/assets/css/display-opinions-*.css
.listradio-wrap .nf-field-element input {
  display: none;
}

However, in 3.6.12 the CSS is:

./wp-content/plugins/ninja-forms/assets/css/display-opinions-*.css
.listradio-wrap .nf-field-element input {
  display: inherit;
}

Overriding the CSS in ./wp-content/themes/…/style.css also hides the checkbox:

.nf-form-content .listradio-container .nf-field input[type="radio"] {
    display: none;
}