Deleted certificate keeps on reappearing in my Keychain. What can restore it?

Hi there,

I recently renewed a certificate I use, among other things) to directly sign-in on password-pretected website at CERN (e.g. collaboration web pages). I deleted the expired certificate from my keychain, and installed the new one: everything seems to be working fine.

The weird thing I'm experiencing since I did all these actions is that every morning I find again in the Keychain the old expired certificate I deleted (?!?), like some process was restoring it. I tried to monitor what could do that without much success, and googling the problem lead to nothing (there seems to be a known issue with Xcode restoring expired certificates, but I never use Xcode, and I don't have developer profiles installed). The thing is rather annoying, because having 2 similar identities, one valid and another expired, seems to trouble Safari, and I cannot really use the automatic login unless I re-deled the expired certificate. Ditto, I have to do it again every morning, since it seems to resurrect somehow...

I tried to lock the login keychain, but using the machine is then impossible (e.g. Mail.app ask for access every time it looks for new mail). I had certificates installed on my iPhone, so I thought that could be the source (the iPhone certainly syncs overnight) and I deleted them, since anyway certificate authentication from iOS on CERN website is not working (yet?). It dod not really helped, tough.

Any suggestions?

I'm running OS X 10.8.2, Keychain access v. 7.0.

Thanks! M.