I keep the main repo on mercurial but made a clone with hg-git for git lovers.
The problem is that in the mercurial repo I went back to a previous commit, created a new anonymous branch and closed the old one. (Reason: postpone development of a feature)
After that I saw that hg-git stopped working.
I tried even to force the commit but still not succeeded.
Ok...finally founded the answer on another hg-git related question
So it seems that you have to update the "master" bookmark to current branch.