Binding issue between choice in XML and e-form fields

Hi everybody,

I am unable to well bind my XSD schema (containing choices) with fields in a subformSet of my e-form.
Here is the complexType of the instance i would like to bind :

(where Months is a complex type and Quarters is a collection of the Quarter complex type).

After having created a new eform, imported my XSD file and dragged and dropped the entry that corresponds to the type above, I get a structure like that in my form's hierarchy:

[...]
Period
(Untitled Subform Set)
(untitled Subform)
Date
Months
StartMonth
EndMonth
Quarters
Quarter
Year
Quarter

Then, I switch to the 'PDF preview' view, and I get only the Date element shown (ok, as the choice is an exclusive one).

My problem is that i would like to be able to choose which one of the choices is enabled to:
- display the right sub-field(s) collection and let the user fill it (Date, Months Xor Quarters).
- choose which one of the choice has to be serialized when I export data in an XML file.

I've tried to use the setInstances() function on several different parts of my hierarchy but it doesn't seem to work.

What is wrong ?

Many thanks in advance.