It looks like there is a bug in Fluidity but you can preserve desired order by sorting it like this.

var property = Model.Content.GetProperty(alias);
var desiredOrder = property.DataValue.ToString().Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries).Select(x => int.Parse(x));
var data = property.GetValue<IEnumerable<object>>().Cast<FluidityModel>();
var orderedData data.OrderBy(item => desiredOrder.IndexOf(item.Id)).ToList();

For production use you should of course write this in a nicer way.