Windows 10 or the browser. Safari, for example, has an “open safe files after downloading” preference.
hurray @Daniel Taylor !
chrome has a checkbox that says always open files after downloading, you cannot see this though as the files download too fast
and there is no way to deselect it from the settings. you have to hand-edit the preferences file and switch it off.
but now it downloads the files as expected.
thankyou for your help everyone.