apt-get wants to Downgrade some packages

[Markus]

APT:efault-Release "testing";
APT::Cache-Limit 10000000;
Apt::Get::Purge;

I'd say that the testing there is why your getting testing packages unless you specify unstable.
Did you tell synaptic to get from unstable?
I don't suppose downgrading the packages will do much harm, but then again, I have never downgraded as I run a pure unstable so I can't tell for sure.