How could passwords on OSX keychain for one user end up in another? Our home MacBook has two users on it: my wife's and mine.  This morning we noticed when logged in as my wife's user that in the KeyChain Access it has all of my web passwords.  Including passwords I only use on my work laptop.  How is this possible?

To clarify exactly what's going on let's define some things:


MacBooks

Home-macbook
Husband-work-macbook

Apple/iTunes accounts

Wife-apple-account
Husband-apple-account

OSX users on home-macbook

Wife-osx-user (uses Wife-apple-account)
Husband-osx-user (uses Husband-apple-account)

OSX users on work-macbook

Employee-osx user (uses Husband-apple-account)



So this is what happened exactly:  On Home-macbook, logged in as Wife-osx-user, we could see passwords in the KeyChain Access program that were only ever used on work-macbook as Employee-osx.

Now if Employee-osx passwords showed up on Home-macbook when logged into Husband-osx-user, that could make some sense.  But why are the passwords being shared between users?  Are they linked through OSX somehow and can I turn that off?

One important note is that this home-macbook was recently upgraded from Snow Leopard to Yosemite.

Update

When I delete these passwords from the KeyChain Access app, they almost immediately are re-added automatically!  How can I stop this?!
The problem is that I have logged into Chrome under wife-osx-user.  Chrome saves passwords into keychain.   And then keychain makes those available to Safari.  Not AT ALL the desired behavior but I suppose it makes some sense.