zerotohero,
I have the same result BUT the only 'starred' (required) item to upload seems to be the CV and I remember that only a CV was required last time (late 2011) too. If you just upload a CV then check the box saying the section is completed you are able to submit the application sans covering letter with no problem.
So it looks like the covering letter is not a requirement and can't be submitted anyway (unless it is a bug as you say)...unless anyone disagrees?