Buttons on control bar/panel are not visible

[Christopher Barrington-Leigh]

Launching ardesia from the command line gets me drawing nicely, but the vertical white bar that appears has no buttons. It's all white. Mouseover shows me the tooltips, and clicking on some seems to work (changing colour, for instance), but the buttons are not rendered.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: ardesia 1.1-2
ProcVersionSignature: Ubuntu 3.19.0-33.38-generic 3.19.8-ckt7
Uname: Linux 3.19.0-33-generic x86_64
ApportVersion: 2.17.2-0ubuntu1.7
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Nov 11 10:50:26 2015
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-03-28 (227 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Beta amd64 (20150325)
SourcePackage: ardesia
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

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

[Koen Roggemans (koen-roggemans)]

Same on Xenial after upgrade from Trusty

[Koen Roggemans (koen-roggemans)]

Purged and reinstalled: no improvement

ardesia -V
Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
Enabled Device in screen 2. 0x1ea3ab0: "Virtual core pointer" (Type: 0)
DEBUG: Annotation window get screen-changed event
DEBUG: Annotation window get configure event (1366,768)
Clear screen
The save point /tmp/ardesia/ardesia_project_2016-4-9_11:43:50/images/ardesia_1_vellum.png has been stored in file
Acquire grab
DEBUG: Annotation window get configure event (1366,768)
DEBUG: Annotation window get configure event (1366,768)
DEBUG: Annotation window get configure event (1366,768)
DEBUG: Annotation window get configure event (1366,768)
The pen with colour FF0000FF has been selected
The pen with colour FF0000FF has been selected
The pen with colour FF0000FF has been selected
The pen with colour FF0000FF has been selected
The pen with colour FF0000FF has been selected
The pen with colour FF0000FF has been selected
DEBUG: Annotation window get expose event
Restore surface
The save-point /tmp/ardesia/ardesia_project_2016-4-9_11:43:50/images/ardesia_1_vellum.png has been loaded from file
The pen with colour FF0000FF has been selected
The pen with colour FF0000FF has been selected
The pen with colour FF0000FF has been selected
Release grab
The pen with colour FF0000FF has been selected