greybird menus and buttons don't rend properly after LTS upgrade

[GridCube]

After upgrading from LTS 16.04 to 18.04 the greybird theme menus do not render properly, buttons have no shadows and hovering with the cursor doesn't highlight options.

examples of errors are attached to the bug report and in this imgur album:
https://imgur.com/a/DHJbs

this error is not present on different themes provided

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: greybird-gtk-theme 3.22.8-1
ProcVersionSignature: Ubuntu 4.4.0-119.143-generic 4.4.114
Uname: Linux 4.4.0-119-generic x86_64
ApportVersion: 2.20.9-0ubuntu2
Architecture: amd64
CurrentDesktop: XFCE
Date: Sat Apr 7 14:06:48 2018
InstallationDate: Installed on 2016-02-13 (783 days ago)
InstallationMedia: Xubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
PackageArchitecture: all
SourcePackage: greybird-gtk-theme
UpgradeStatus: Upgraded to bionic on 2018-04-06 (0 days ago)

[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/1762026

[GridCube (gridcube)]

bug seems to be fixed after today's update

[Theo Linkspfeifer (lastonestanding)]

The final release still has the same version 3.22.8-1, so not a bug in this package.