OK, I launched the new version (gace5a0113-patchB), set the font size to 12pt (which made the text huge as before), and then relaunched it. The resulting editor window is this:
The debug output is:
GDK_SCALE is 1
Resolution / Before: 72.000
Resolution / After : 72.000
"Non-Default" font size(12) * scale(1) / fontScale(1.000)
CSS:
* { font-family: Helvetica; font-size: 12pt}
>>> RTScalable::init start
setDPInScale(72.000, 2) -> DPI: 144.000, Scale: 2
<<< RTScalable::init end