SharePoint SPList.LastItemModifiedDate And SPWeb.LastItemModifiedDate Are UTC Time

In SharePoint API, a SPList object has a LastItemModifiedDate property that indicates the last item modified time. The MSDN description for this property is: Gets the date and time that an item, field, or property of the list was last modified.

We use this property to validate the memory cache in one project, but the cache is not properly updated when the list item is changed. Finally we figured out this property returns a UTC time not a local time. To correct the issue, simply use the ToLocalTime method:

DateTime listLastUpdate = list.LastItemModifiedDate.ToLocalTime();

Similarly, SPWeb.LastItemModifiedDate is also UTC time, and you need to convert it to local time manually when you use it in the code.

In fact, all DateTime values stored in SQL Server, such as list item's "Modified" time, are in UTC format. SharePoint will convert it back to local time:

SPListItem item = list.Items[0];
DateTime modifiedTime = Convert.ToDateTime(item["Modified"]);

I don't see any reason why this LastItemModifiedDate property is using UTC format. My guess is that the time is not parsed by database value, instead is created something like this in code behind:

DateTime listModifiedDate = new DateTime(value from database);

Is it a bug only existing in SharePoint 2007? I checked the latest SharePoint 2010 RTM release (build number 14.0.4762). To my surprise, they're still UTC time. Maybe MS should document them or give explanation for any such inconsistent stuff inside API.