Form containing file-field will not post on Safari 11.1

Hello

I think I found a bug.

Forms containing file-fields will post normally in all browsers except Safari on iMac. I tested on several iMac’s from different people. All were running Safari 11.1. Tested with iPhone and iPad as well, but all goes well on these devices.

Without this specific field the form posts normally. Only when adding a file-field the error occurs. Even when the field is not filled, or not required.

I’m getting a 503-error as ajax-response about 15-20 seconds after submitting the form. The arrow-gif keeps running infinitely.