Spring MVC form hidden field appears null only in IE

Question

In a simple sample, I have two models DailyTimesheet and MonthyTimesheet:

class DailyTimesheet {  
    // other properties  
    MonthlyTimesheet timesheet;  
}

class MonthlyTimesheet {}  

In the form, I have the code as:

<form:form action="/update/timesheet" method="POST" 
  modelAttribute="dailyTimesheet">  
    <form:hidden id="timesheet_id" path="timesheet.id"/>
    <!-- Other form stuff -->
</form:form>

In the controller, first I resolve the MonthlyTimesheet instance by:

Long timesheetId = dailyTimesheet.getTimesheet().getId();
MonthlyTimesheet timesheet = MonthlyTimesheet.findTimesheet(timesheetId);  

and then I do the rest for the business. In Firefox and Chrome, it works fine. However, in Internet Explorer, I get an NullPointerException on dailyTimesheet.getTimesheet().getId() that means the timesheet instance for the dailyTimesheet is null. Looks strange as if the IE sends the data in a way that Spring MVC Binding does not bind the value to the related property.

Thanks for your help in advance.