I've finally solved the issue employing a HashMap, rather than a set. So, in my controller, I'm filling the map with the List of listFunctEnabled for every role (key of the hashmap) For instance: map[ROLE_ADMIN] = {Funct1, Funct2, Funct3}
The RoleForm remains the same, so the selected items are stored in listFunctEnabled property.
Now, in the JSP, I access that with the following:
<form:form method="post" id="roleForm${role}" modelAttribute="roleForm${role}" action="roles.html">
<fieldset>
<form:hidden path="roleCode"/>
<div class="pickList">
<fieldset class="pickItems">
<legend >Enabled</legend>
<form:select path="listFunctEnabled" id="combo1" size="5" multiple="true">
<form:options items="${map[role]}" />
</form:select>
</fieldset>
</div>
</fieldset>
</form:form>
And no problems with that solution. I hope could be useful for someone else.