I suggest that you download the Xubuntu 18.10 daily ISO, then boot into live mode and check if the issue with the open source driver is present too.
Another thing to test is to see if disabling the builtin compositor (Settings > Windows Manager Tweaks > Compositor) eliminates the glitch. -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to xserver-xorg-video-nouveau in Ubuntu. https://bugs.launchpad.net/bugs/1775212 Title: Windows not painted completely since 18.04 Status in xfwm4 package in Ubuntu: New Status in xserver-xorg-video-nouveau package in Ubuntu: New Bug description: Since upgrading to Xubuntu 18.04, the graphics on my desktop are broken. It seems to affect all windows and menus, which are painted incompletely, or with the wrong colours. It seems to get progressively worse, to the point of making programs unusable because entire sections of the user interface are missing, so this should have high priority IMHO. I will attach a few screenshots as examples. ProblemType: Bug DistroRelease: Ubuntu 18.04 Package: xfwm4 4.12.4-0ubuntu1 ProcVersionSignature: Ubuntu 4.15.0-22.24-generic 4.15.17 Uname: Linux 4.15.0-22-generic x86_64 ApportVersion: 2.20.9-0ubuntu7.1 Architecture: amd64 CurrentDesktop: XFCE Date: Tue Jun 5 17:29:02 2018 InstallationDate: Installed on 2017-03-23 (439 days ago) InstallationMedia: Xubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215) SourcePackage: xfwm4 UpgradeStatus: Upgraded to bionic on 2018-05-14 (22 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xfwm4/+bug/1775212/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp