Typing "C-h k x" to try to find out what "x" is bound to fails:
Debugger entered--Lisp error: (wrong-type-argument stringp t)
describe-function-1(self-insert-command)
describe-key("x" 1 nil)
call-interactively(describe-key)
The same happens whichever key sequence I try to describe.
I've tried a "make bootstrap" but the problem persists.