Getting '--MORE-- unknown key 0xff detected' when booting Thinkpad

Hi everyone,

I am running Trisquel 10 on a Thinkpad with coreboot.

I inserted a usb with another OS into my laptop today and restarted my computer, trying to boot into that OS.

I guess I pressed 'F2' one too many times because I just saw '--MORE-- unknown key 0xff detected' and this was the dialogue that kept going below the regular Grub menu (I think). I have attached a screenshot.

When I remove all usbs (including the dongle for my mouse), the laptop boots properly without this dialogue.

Any help for me?

Best,