Kubuntu bionic beta 1: laptop screen set to minimum brightness

[Glen Ditchfield]

I booted from a USB drive made from the Bionic Beta 1 Kubuntu Desktop AMD64 ISO. I have powered off before booting, and also restarted from Kubuntu 17.10. Either way,
- the screen starts at normal brightness (about 50%).
- The "keyboard" screen appears, again at normal brightness.
- A couple of console messages appear, and screen brightness drops to the minimum value.
- The Kubuntu "K" splash screen and the Welcome "Try Kubuntu"/"Install Kubuntu" chooser appear, at minimum brightness.
- I choose "Try Kubuntu" and the live desktop appears, at minimum brightness.
- Strangely, the Kubuntu Desktop's "Battery and Brightness" says that the screen is at 100% brightness. As soon as I move the brightness slider, the screen brightens up to match it.

The laptop is an HP EliteBook 8440p, with Intel graphics.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: syslinux (not installed)
ProcVersionSignature: Ubuntu 4.15.0-10.11-generic 4.15.3
Uname: Linux 4.15.0-10-generic x86_64
ApportVersion: 2.20.8-0ubuntu10
Architecture: amd64
CasperVersion: 1.389
CurrentDesktop: KDE
Date: Fri Mar 9 01:13:57 2018
LiveMediaBuild: Kubuntu 18.04 LTS "Bionic Beaver" - Alpha amd64 (20180306.1)
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: syslinux
UpgradeStatus: No upgrade log present (probably fresh install)

[Ubuntu QA Website (ubuntuqa)]

This bug has been reported on the Ubuntu ISO testing tracker.

A list of all reports related to this bug can be found here:
http://iso.qa.ubuntu.com/qatracker/reports/bugs/1754536

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.