Migrated InfoPath Workflow form (2007 to 2010) changes its behavior with extended properties

Question

Hello,

I have a InfoPath form that I use in a custom Visual Studio Workflow.

I use the CreateTaskWithContentType activity to create task associated with the custom form.

In the workflow code, I use CreateTaskWithContentType.ExtendedProperties to pass values to the form :

myCreateTask.ExtendedProperties = new NameValueCollection  
{
   { "Param1", "Value1"},
   { "Param2", "Value2" }
};

Then, in the form code, I retrieve the values using (note the ows_ prefix):

XPathNavigator secondDataSource = this.DataSources["ItemMetadata"].CreateNavigator();
secondDataSource.MoveToFirstChild();

string param1 = secondDataSource.GetAttribute("ows_Param1");

Everything was working fine on SP 2007.

However, we recently migrated the farm to SharePoint 2010. The forms has stopped to works as expected. After some digging and headache, I finally discovered than some parameters are prefixed with owsextended_ while other properties are still using the prefix ows_.

For example, in the same task, I will have to seek for ows_param1, and owsextended_param2.

What can cause this changed behavior? What is differentiating the parameters to produces either ows_ or owsextended_ prefix?

Please note that the itemmetadata schema is actually showing ows_Param1 and ows_Param2 as attributes.

Thanks in advance for the help

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