Time format in the time header resets to 24hour after update() call

I'm using the mvc scheduler, and displaying only single day.
For the time header display, I'm doing the following to get the 12 hours format (AM/PM), and also setting TimeFormat = TimeFormat.Clock12Hours in the config:

protected override void OnBeforeTimeHeaderRender(BeforeTimeHeaderRenderArgs e) {
if (e.IsColGroup) {
e.InnerHtml = TimeFormatter.GetHour(e.Start, TimeFormat.Clock12Hours, null);
}
}

Everything renders fine, with the 12 hour format, but when i call the update() method on the DayPilot object, the time format changes to 24hour (displaying 0-23).

Am I missing something?