Vertical text with text-anchor is converted incorrectly

Migrated from https://bugs.launchpad.net/inkscape/+bug/1893644

Summary:

<svg viewBox="0 0 120 120" xmlns="http://www.w3.org/2000/svg">
    <text text-anchor="end" style="writing-mode: vertical-rl;text-orientation: upright;">
        <tspan y="60" x="40">A B</tspan>
        <tspan y="60" x="75">R Y C</tspan>
        <tspan y="60" x="110">A B</tspan>
    </text>
    <!-- Materialisation of anchors -->
    <circle cy="60" cx="40" r="3" fill="red" />
    <circle cy="60" cx="75" r="3" fill="red" />
    <circle cy="60" cx="110" r="3" fill="red" />
    <style><![CDATA[
  text {
    font: bold 5px Verdana, Helvetica, Arial, sans-serif;
  }
  ]]></style>
</svg>

Steps to reproduce:

inkscape --export-text-to-path --export-type=svg --export-filename='convert2.svg' 'convert.svg'

What happened?

This content is displayed wrong after I run cmdline Inkscape to convert content above from convert.svg file to convert2.svg file, may be text-anchor is not working with writing-mode: vertical-rl.

Version Info:

- Inkscape Version: n/a
- Operating System: n/a
- Operating System version: n/a

Migrator's Notes:

Without a reference screenshot from the author for control, I can't tell if this is a bug (and on whose part) or malformed svg code. EDIT: svg passed W3C Validation with only one warning (No Character encoding declared at document level) .

Saving the author's code as an svg file and opening in Inkscape I see this...

In Inkscape GUI before and after CLI conversion...

In macOS QuickLook...

In Firefox...

In Safari...

• Additionally, in Safari, when convert.svg is loaded and I click away from Safari, the text from the first two columns disappears!

Tested on 1.1.0-dev (48d18c81, 2020-07-08), macOS 10.13.6 (17G12034).