UserAgent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0

Example URL:
http://test.csswg.org/suites/css-text-3_dev/nightly-unstable/html/text-transform-fullwidth-002.htm

Steps to reproduce the problem:
Reduced self-explanatory test:

http://test.csswg.org/suites/css-text-3_dev/nightly-unstable/html/text-transform-fullwidth-002.htm

What is the expected behavior?
Reference file:

http://test.csswg.org/suites/css-text-3_dev/nightly-unstable/html/reference/text-transform-fullwidth-002-ref.htm

or (better)

http://test.csswg.org/source/css-text-3/text-transform/text-transform-fullwidth-002-ref.xht

What went wrong?
Basic support of text-transform: full-width (see issue 684968) is required to begin with, before tackling this issue. So, this issue depends on issue 684968.

Does it occur on multiple sites: N/A

Is it a problem with a plugin? No 

Did this work before? No 

Does this work in other browsers? Yes

Chrome version: 57.0.2986.0  Channel: dev
OS Version: 
Flash Version: Shockwave Flash 11.2 r202

Since full-width Latin characters are typeset upright, then they should not be rotated 90degrees in vertical writing-modes, unless they are affected by text-combine-upright, unless text-combine-upright applies to such Latin characters.

Section 9.1.3.1 Full-width Characters
https://www.w3.org/TR/css-writing-modes-3/#text-combine-fullwidth
in the text of EXAMPLE 17, we can read:
{
since the "2" is only one typographic character unit, it will be transformed to a fullwidth "２". Since the "2010" was not combined, its digits, too, will be transformed to fullwidth "２０１０"; and being fullwidth, they will be typeset upright
}