Double click in protected document to check in checkboxes?

Hi there,
I have a really strange problem in company I work for. We have just started to upgrade from Office 2013 to 2016. Our Intranet portal runs in Microsoft Explorer. The issue is this:

From a link in our Intranet portal a .dotm file is launched. The code in this file shows a menu where the user can select different products. After the selection, different .doc or .docx files are inserted into the same document, to form a larger document with products. The document is then protected, so the user can only fill in fields and use checkboxes. It has always been enough to click 1 time in a checkbox to select or deselect it, but after we have upgraded clients to Office 2016, users have to doubleclick in a checkbox to select/deselsect it. Downgrading to 2013 and the issue disappears again. The even stranger part is, that if the user closes Internet Explorer while the document is open, the issue disappears right away, and a single click is enough.

Anyone has any idea why this is?

Best regards
Lars