Safari "Save As..." dialog not saving tags

Safari is no longer saving Finder tags when I try to save a web page as archive. It will save tags if I save as page source. I think this behaviour is new to Mojave. To be clear: on a wepage, click "File" drop-down menu, then "Save As..." then for "Format" select either "web archive" or "page source". In both cases, one can fill in the "Tags" field at the top of the save dialog. But if I have selected "web archive" the tags do not get saved, whereas if I select page source they do.

I've tried this on two computers running 10.14.5. Do others see this behaviour, and if so is it a security feature of some kind?