Thanks Nicolai for your quick answer. I'm looking forward for the fix.

However, my calendar (not your widget but Nokia's Calendar application) is showing some of the birthdays but not all of them. As I guess you have some knowledge about events and tasks internals, I would like to know your opinion about what could be causing this part of the problem. Maybe in addition to the problem in the widget I have a corrupted calendar database? May this be impacting the widget behavior?