minimize & maximize buttons invisible in high-visibility theme when window has focus

[jimav]

The "minimize" and "maximize" buttons in the current window border are invisible when using the "High Contrast" system theme.

STEPS TO REPRODUCE:

1. Open Appearance manager (WindowsKey->Appearance).
2. In the "Look" tab, set Theme to "High Contrast"
     (window border background should change to white)
3. Give focus to any window on the desktop

RESULTS: The "minimize" and "maximize" icons become invisible in the top window decoration of the focused window.

EXPECTED: Icons remain visible at all times.

P.S.
I have focus-follows-mouse enabled (don't know if that matters).

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: gnome-accessibility-themes 3.14.2.3-0ubuntu1
ProcVersionSignature: Ubuntu 3.19.0-30.33-generic 3.19.8-ckt6
Uname: Linux 3.19.0-30-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.17.2-0ubuntu1.5
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Oct 1 19:34:49 2015
Dependencies:

InstallationDate: Installed on 2013-08-06 (787 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
PackageArchitecture: all
SourcePackage: gnome-themes-standard
UpgradeStatus: No upgrade log present (probably fresh install)