OSX Mavericks: package installs fail, Gatekeeper seems broken

For some reason my OSX Gatekeeper seems to be broken.

Every time I try to install software I get: the package was signed with a certificate that has expired.

However, when looking at the certificate chain, everything seems to be correct.

The key chain also has the Developer ID Certification Authority which seems to be both current and trusted.

Any idea what this could be about?

Thanks!