Hi, I found this bug because I had a similar problem on a Lenovo x250. I haven't tried an updated kernel, but I did find that updating to the latest BIOS release made things work again.
Unfortunately I didn't note the contents of /sys/bus/serio/devices/serio1/firmware_id before I updated, but after the update it is "PNP: LEN0046 PNP0f13". Hope this helps -d
