I've upgraded a t400 that used to run libreboot_r20160818_grub_t400_8mb to seabios_withgrub_t400_8mb_libgfxinit_corebootfb_usqwerty.rom

If it has a VGA monitor plugged in at the time of reset or powerup, only the external monitor is usable until the next reset. 

The LCD monitor is still power up, and displays a uniform, single-color screen, that keep changing colors every few seconds.  If it is powered off (say with xrandr), it goes dark, and if it is powered back on, the changing colors return.

That is an undesirable and inconvenient regression.

It is not critical, because there's an easy workaround: unplug the VGA cable when powering up the computer, plugging it back in shortly thereafter.  Then, both monitors work as desired.