You could potentially workaround this issue for at least running KDE session (not for KDM though) by using xrandr in Xsession startup script. You would need to add new file /etc/X11/Xsession.d/35fix-displaysize with the following content:
/usr/bin/xrandr --fbmm 330x210 || true
You need to replace 330x210 with actual size of your display in millimeters (mm).
You could potentially workaround this issue for at least running KDE session (not for KDM though) by using xrandr in Xsession startup script. You would need to add new file /etc/X11/ Xsession. d/35fix- displaysize with the following content:
/usr/bin/xrandr --fbmm 330x210 || true
You need to replace 330x210 with actual size of your display in millimeters (mm).