Comment 12 for bug 2061373

The grub patch linked seems similar in that grub is not clearing the mode correctly when you enter grub text mode, i.e. the menu is drawn/you enter the console.

However I don't think you are entering the text mode in grub at all, but you jump straight to the kernel as part of flicker free boot - our grub is specifically patched to avoid mode switches.

So I'd have expected the kernel to request text mode before dumping stuff there or nothing requesting text mode and plymouth popping up with a nice spinner on top of that background that the firwmare rendered.