The method driver /usr/lib/apt/methods/https could not be found. I hope the latter will be fixed by apt-1.2.1, which I haven't tried yet.
It seems that this issue is fixed by apt-1.2 but it's replaced by
another message:
- Bug#808802: #808802 synaptic: Can't drop privileges for downl... Michael Vogt
- Bug#808802: #808802 synaptic: Can't drop privileges for ... Tsu Jan
- Bug#808802: #808802 synaptic: Can't drop privileges ... Michael Vogt
- Bug#808802: #808802 synaptic: Can't drop privile... Tsu Jan
- Bug#808802: #808802 synaptic: Can't drop privile... Tsu Jan
- Bug#808802: #808802 synaptic: Can't drop privileges for ... Tsu Jan