Updating OS X Mavericks without entering payment information?

Question

A while back I created a Apple ID for my self on a loaned iPhone 4 at work. Recently my partner upgraded her MacBook Pro to Mavericks, and being the IT guy in the house, I installed the first few updates that popped up after signing in with my Apple ID on my user account.
Today she received more update notifications on her account, so she proceeded to install them. She was asked for my account password. Strange that that carries across user accounts, but okay... clicked the Store menu, Create Account. All goes fine, until the billing information step. Neither of us has a credit card, nor do we understand why one is needed for system updates.
I looked around for a solution and came across this article in Apple's knowledge base:
Creating an iTunes Store, App Store, iBooks Store, and Mac App Store account without a credit card. It suggests using "None" as the payment option, but such an option does not show up for us.

Now I know similar questions have been asked before, but none seem to answer this question: How to update Mac OS X Mavericks without entering any payment info?

Also: Why can I install updates even though I haven't entered any billing info either? We don't have any iOS devices to try to duplicate the results.

Answer 1

I think I solved it. The reason my partner was asked for an Apple ID in her user account in the first place, was because I was signed in to the App Store with my ID under my user account. After signing out of the App Store on my account and logging back into her account, she was no longer asked to enter my password or an Apple ID altogether anymore.

I would consider this a pretty strange bug, an apparently rare but easily reproduced one at that, but perhaps this will help other people who share a Mac.