Boot splash screen and shutdown splash screen ou of sync

It’s not a big problem just looks bad in that the splash screens for booting and shutdown are
out of horz sync. Once the OS is booted the login screen is fine

I just can’t find where this is controlled.

yeah !! It’s same with my installation as well. Are you referring to the start-up screen ? Splash screen in displayed after successful login (correct me if I am wrong).
If you are referring to to start-up screen (green colored with lizard), then, there is no control setting for it as far as I know. Since it’s still a test version, hopefully
it will be set fine in stable release. Just a minor glitch IMHO.