I use the simple coreboot config https://github.com/merge/skulls/blob/master/x230/free-defconfig-555419f356
on today's coreboot master branch HEAD (403f433238), using SeaBIOS 1.12.1.
When choosing memtest86+ in SeaBIOS' menu, "Booting from CBFS" gets printed but nothing else happens.
Booting into nvramcui or coreinfo works though.
(earlier, at least on coreboot 555419f356, using the same version of SeaBIOS, things were fine).
Can you imagine why?