The bug is that both g++-4.1 and g++-4.2 Provide c++abi2-dev. The dependency resolver used by autopkgtest and apt-get doesn't do automatic installation of ambiguous dependencies, while pbuilder's does.
(This is just one of the ways in which retesting with pbuilder doesn't always exactly reproduce autopkgtest bugs.)
The bug is that both g++-4.1 and g++-4.2 Provide c++abi2-dev. The dependency resolver used by autopkgtest and apt-get doesn't do automatic installation of ambiguous dependencies, while pbuilder's does.
(This is just one of the ways in which retesting with pbuilder doesn't always exactly reproduce autopkgtest bugs.)