I have applied the Group By Month view type to a view. I am using a CCK Datestamp field. I am sorting by the CCK Datestamp field. My view presents the nodes (which all have a March 2008 datestamp) grouped by December 1969.

Let me know if you'd like to see an export of my view.

This is happening with both the 5.x-1.0 and the 5.x-1.1 versions.

I am using Drupal 5.5 with PostgreSQL.