Hello world,
This issue is solved now.
My workaround :
Define a Content Type for each fields.
Add extended properties to the task with the name of your field : myTaskProperties.ExtendedProperties["myFieldName"] = "my expected value";
This is the way to pre-fill your form by the code.
To retrieve data from your global infopath form :
I've a method which do that. This method is going to read the xml (my global infopath) and get the value. After that, I add this value instead of "my expected value" above.
If you want more explanation or code, don't hesitate to contact me ;-)
Cheers
Skilpit