here is a screenshot of the settings
I could analyze the situation as this
1. i went to one of my old logs its name is April 2010 (i set the logs by mail account)
2. i set my laptop date to April 2010
3. right clicked the same contact from the main menu in WLM and shoot it opened
4.
the result: when u right click a contact it seems like it searched for a log in the current month if there is no file for the current month it says there is no logs for that contact..