When I reduce the font size the tops of the letters get chopped off

[Kingsley Tart]

When I run kompare with the font set to Deja Vu Sans Mono 10pt, the display is fine (http://quitebig.com/temp-pics/ubuntu-kompare-bug/kompare-1-deja-10pt.png)

If I reduce it to 9pt then it chops off the tops of the characters (http://quitebig.com/temp-pics/ubuntu-kompare-bug/kompare-1-deja-9pt.png)

It also happens with bitmap font Fixed Misc 9pt (http://quitebig.com/temp-pics/ubuntu-kompare-bug/kompare-fixed-misc-9pt.png)

It's fine with "Courier 10 pitch" 11pt (http://quitebig.com/temp-pics/ubuntu-kompare-bug/kompare-courier-10-pitch-11pt.png) but it breaks with 10pt (http://quitebig.com/temp-pics/ubuntu-kompare-bug/kompare-courier-10-pitch-10pt.png)

It's fine with FreeMono 12pt (http://quitebig.com/temp-pics/ubuntu-kompare-bug/kompare-freemono-12pt.png), but breaks with 11pt (http://quitebig.com/temp-pics/ubuntu-kompare-bug/kompare-freemono-11pt.png) and 10pt (http://quitebig.com/temp-pics/ubuntu-kompare-bug/kompare-freemono-10pt.png)

I've also noticed that if you make the font too big, it doesn't allow enough vertical height, eg using Hack 17pt (http://quitebig.com/temp-pics/ubuntu-kompare-bug/kompare-hack-17pt.png)

$ lsb_release -rd
Description: Ubuntu 18.04.1 LTS
Release: 18.04

$ apt-cache policy kompare
kompare:
  Installed: 4:17.12.3-0ubuntu1
  Candidate: 4:17.12.3-0ubuntu1
  Version table:
 *** 4:17.12.3-0ubuntu1 500
        500 http://gb.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status

The same thing also happens on my laptop (and also did with Ubuntu 16 LTS). Both machines use Nvidia cards, though I'm using the free driver instead of Nvidia's own because the specific Nvidia driver only supported one monitor and only ran at 1024x768.

I installed this as kubuntu, in case that matters.

[Kingsley Tart (itchy-spock-ears)]

Every font I've tried suffers from these vertical spacing issues. It is not limited to the fonts I mentioned in the initial report.

[Kingsley Tart (itchy-spock-ears)]

I have just found that if I leave kompare set to a font that gets the wrong vertical alignment, then restart it, it displays properly in the new instance. The issue only seems to occur in the instance of kompare in which you first make the change.