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.
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.