UEFI and loader.efi in base/head past r355103

I updated the loeader.efi stored in the ESP of my laptop, Lenovo 
ThinkPad E590T (20NB), running boot firmware 1.22, as I wanted to try 
out base/head r355441.

As soon as I press a button, say 2 or 3, the loader freezes. 
Ctrl+Alt+Delete is being recognized.

I have tried loader.efi from the latest official current snapshot, 
20191212, r355634, only to get the same result.

Luckily, I had the wisdom of keeping the previous loeader.efi on hand. 
I have since expanded this to include an extra copy of the last known 
good loader, which will be updated less frequently.

loader.efi from r355103 are not affected and is the one I use today.

Any of these commits could be the culprit:

r355617, r355441, r355392, r355347, r355308, r355168, r355167, or, 
355132.

r355347 is a good candidate as it affects the reading of keystrokes.
I have therefore CC-ed tsoome_at_.

In the meantime, I'll revert to r355346 and try that loader.efi.

-- 
Trond.