You can't create tags when using the mobile version of the site; when you attempt to do so, you're greeted with the following error message:
New tags cannot be created from the mobile site. The tag '[tag name]' is new.
However, I was able to 'circumvent' this by switching to the new responsive site. This seems a little inconsequential: if not being on mobile is really that important, the check should be added to the responsive site as well (and perhaps trigger on certain User-Agent values); if it's not, it's better to remove that check altogether (it could take a while for the review pages to become fully responsive). I don't really have a preference, I just want the inconsistency to be resolved. Do you have any thoughts/arguments to prefer one option over the other?