When you create a new gallery (/manage/gal), you have the option to set the Gallery Date. If you set the Gallery Date in the Create Gallery page, it doesn't actually store the date. However, once you've created the gallery, you go into Manage Gallery. If you set the date there, it stores it correctly.
The bug here is that it should have stored it from the Create Gallery page.
Shout if you need more information :-)