Incorrect Modified Dates on SharePoint Online for clients in other timezones

Question

I've run into a strange problem with SharePoint Online.

When updating or creating entries in a list using the Client Object Model, the modified date on the affected list item seems to be stored with the wrong timezone.

Our Office 365 server is at UTC -7 (I assume it's probably on Redmond time, even if it's not actually physically there), and I am at UTC +1. If I create a record using C# on the server, the modified date is stored with the current date and time at UTC -7. However, if I store a record from the client using JavaScript, the record is stored with my current time, but is also at UTC -7!

e.g.

if current time        = 13:07 GMT
my local time          = 14:07 UTC +1
storing on the server  = 06:07 UTC -7
storing via the client = 14:07 UTC -7  (e.g. 8 hours in the future!)

I am not setting the modified date directly - I'm relying on SharePoint to track this information correctly.

My client script looks like this:

function addRow() {
    //Create a new record
    var context = SP.ClientContext.get_current();
    var extList = context.get_site().get_rootWeb().get_lists().getByTitle(options.listTitle);

    var itemCreateInfo = new SP.ListItemCreationInformation();
    var listItem = extList.addItem(itemCreateInfo);

    //Set the values
    listItem.set_item('Current', data.query.results.quote.LastTradePriceOnly);
    listItem.set_item('Title', 'results');

    listItem.set_item('TradeDate', tradeDate);
    listItem.set_item('TradeDateStamp', tradeDate.getTime());

    listItem.update();
    context.load(listItem);

    context.executeQueryAsync(
        Function.createDelegate(this, addListItemSucceeded),
        Function.createDelegate(this, addListItemFailed)
    );

    function addListItemSucceeded() {
        console.log('Row ' + data.query.count + ' added OK. New ID is ' + listItem.get_id());
    }
    function addListItemFailed(sender, args) {
        console.log('Failed to add row ' + data.query.count + '. ' + args.get_message() + '\n' + args.get_stackTrace());
        console.log(data);
    }
}

Am I doing something wrong? Or is this a bug with SharePoint Online?

Update: The problem occurs when I try to retrieve the value of the Modified date using the Server Object Model:

DateTime lastUpdateDate = DateTime.MinValue;

var web = SPContext.Current.Site.RootWeb;
SPList list = web.Lists[ListName];
SPListItemCollection items = list.GetItems();
foreach (SPListItem i in items)
{
    DateTime modified = (DateTime)i["Modified"];
    if (modified > lastUpdateDate)
    {
        lastUpdateDate = modified;
    }
}

// lastUpdateDate is in the future if a client in a timezone east of Redmond
// updated the data using the client object model

Answer 1

It might be a Localtime to UTC conversion issue. This normally happens when you have timezone differences from the server. Try converting your Localtime to UTC using the SPTimeZone object and then saving it.