I am not aware of any changes that should cause this.
Lukas, for me, with ZA I can't browse from HTTP to HTTPS: email loggins, bank sites, etc.
It's not a deterministic behavior: one time the page loads, others not... In one computer, I give up on teaching the users how to manage it. I just disable WebShield... It's not always stable, in all systems, all the time... Specially whit HTTPs :'(
Oh, I forget, the computer uses a local proxy