Hmm, the package ca-certificates cannot be upgraded into the version 20110421. Synaptic throws an error of broken packages.
Something wrong with ca-certificates
Archived thread 1745657 from Oneiric Ocelot Testing and Discussion (CLOSED). Markdown source: Oneiric_Ocelot_Testing_and_Discussion_(CLOSED)/thread_1745657_Something_wrong_with_ca-certificates.md
Indeed, seems like ca-certificates was synced from unstable without syncing newer openssl too.
The upgraded openssl (1.0.0) solved the dependency issue.