You're not alone... We had the same issues with this platform and were not able to authenticate in pre-boot in any way.
We've ended up deploying this platform with a different encryption solution than our standard MDE.
BTW, we've escalated this issue to Lenovo only recently (after seeing similar issues with the Lenovo ThinkPad 10 Tablet).
I'll let you know if we get any different response from Lenovo on this.
Good luck !
we have the same issues with Lenovo Think Pad Tablet 2 and MDE. Is a solution known for this topic?
Is the tablet running in UEFI Native or Legacy (BIOS) mode? If Legacy (BIOS), the touch screen will likely not function as there are not appropriate drivers available (KB76514).
Please run the UEFI testing tool (KB78050) on this tablet to determine if the protocols are available in the UEFI.
More information about tablets can be found in the Drive Encryption 7.1 FAQ (KB79784).
Our problem is on the Lenovo Helix running windows 7 under legacy mode. OSK is enabled in the policies. I have found out by accident that if you have the stylus out of the device before power on, then the OSK will pop up and you can type with the Stylus.
I am going to open a case with Lenovo as the touch function with stylus and finger as input work perfectly.
I have built a windows 7 machine in UEFI mode but the McAfee PBA screen went all distorted.