An underline/overline/line-through on vertical text now runs down the column, on the correct physical side of the glyphs (css-writing-modes-4's over/under sides), instead of being drawn as a short horizontal stroke across the top.
Latin text is a rotated run under the default (mixed) text-orientation - one ordinary horizontal glyph run reoriented as a whole - so its ink can now be measured and skipped, same as under a horizontal writing mode. An upright run (forced here via text-orientation:upright) has no single natural horizontal layout to reduce to and still draws unbroken - the honestly-partial half of this issue.
left/right pin the underline to a literal physical edge instead of the writing mode's own default under/over mapping. The third column combines underline+overline with a side that would put the underline where the overline normally sits - per css-text-decor-4 §2.5, the overline switches to the opposite edge instead of overlapping it.