It's by design.
To quote from Meta.SE:
Probably because it's really easy to make a typo when using a mobile browser, and they don't want to clutter the tag-space with misspellings, so it's prompting you to recheck.
For legitimate cases, just edit the tag in later when you're not using a mobile browser or switch to the full-site version.
Kevin Montrose, one ...
I can’t speak for the SE Staff, but I would guess the answer is no.
Quoting SE dev Ebenezer Sklivvze on Meta.se question asking for something similar:
Declining as there are no plans to differentiate the sites on mobile (see e.g. the mobile apps).
Since Meta.se is much larger than SFF, and didn’t get an exception, I doubt we’d get one either.