Reversed x/y in tspan with vertical text

[Pike]

When saving vertical text the x,y coords in the resulting text element match where the text was visually placed in Inkscape (accounting for the reversed y axis and the different text start point). However the x,y coords in the automatically-generated inner tspan seem reversed.

In the example below text was placed at x=50, y=200 (document height=297, text width=8, text height=88). The saved text element x,y is 53, 9 which seems correct but the tspan x,y is 2,59 which doesn't correspond to anything.

<text
       xml:space="preserve"
       style="font-style:normal;font-weight:normal;font-size:10.58333302px;line-height:1.25;font-family:sans-serif;letter-spacing:0px;word-spacing:0px;writing-mode:tb-rl;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.26458332"
       x="52.899048"
       y="8.6901445"
       id="text3833"><tspan
         sodipodi:role="line"
         id="tspan3831"
         x="2.1785734"
         y="59.410618"
         style="stroke-width:0.26458332">Vertical text test</tspan></text>

This causes the text to be displayed in the wrong position in Firefox, Chrome and Edge as they position using the tspan coordinates.

Using Inkscape 0.92.2 64-bit on Windows 10 Pro 64-bit.