Meld 3.18.3 and 3.20 on Windows - not showing inserted empty lines

Per subject line - I was using meld very happily with mercurial, then got a new laptop, installed meld, and now if I hit return to insert a blank line in any pane, I see the line numbers update as if there is a blank line there, but the blank like is not shown, eg like this:

720 some source
721 some more source

Now I hit return at the end of line 720 twice, I will see:
720 some source
723 some more source

But, no blank lines shown in between. Am I missing some preference or is my version bust somehow?

Thanks!

This has been fixed in the current development branch, but because the fix is slightly invasive it hasn’t been merged into the 3.20 releases. For now, the workaround is to manually select a fixed-width font in the preferences. See https://gitlab.gnome.org/GNOME/meld/-/issues/453 for more details.