I never bought the temporary insanity, I think Cecil put him on some advanced psychopharmaceuticals and cured his insanity.
Geniuses don’t become monsters just because they’re right and need to go to extremes to prove it, and monsters don’t become docile just because they’re given funding.
That being said, his character survives the downfall of the GDA, so I think he was cured for good, and it’s not an ongoing thing.
Donald is the second in command at a global secret agency. Cecil doesn’t tolerate incompetence, so Donald got that position through merit.
It wouldn’t be difficult for him to have looked at Cecil’s hands at any point in time while he was typing his password and read the keys he’s pressing.
And Donald is a trusted enough associate, Cecil probably wouldn’t go through the motions of obscuring the keyboard from him.