After trying to figure out what was going on, the response to a simple sanity check command said it all:

+ git config --list --global
fatal: $HOME not set

More details filed here:

In my case the debian package was slightly newer (the one that came with Ubuntu 11.10), and jenkins is now controlled using service, and i modified the /etc/init/jenkins file to include

env HOME="/var/lib/jenkins"
with the rest of the environment variables.

On 31 December 2011