[Zope] problem with selection list in ZClass's addForm

[Darran Edmundson]

Property Degree in my ZClass is of type "selection", getting
its choices from the root folder property DegreeTypes.  DegreeTypes
is of type "lines" and has choices ['B.Sc.','M.Sc.','Ph.D.'].

My problem is that the user's choice is not getting set
properly by the class's constructor.  The following is
the relevent snippet from my addForm:

 <SELECT NAME="Degree"><dtml-in DegreeTypes>
    <OPTION VALUE="<dtml-var sequence-index>"><dtml-var
sequence-item></OPTION>
 </dtml-in></SELECT>

I've looked at the REQUEST variable being passed from
the form and it is an integer corresponding correctly
to the index of the selected Degree.  I have tried casting
this to string and to int but to no avail - it always defaults
to the first element of DegreeTypes.  (I can subsequently set
it to any of the 3 choices in the intance's Properties sheet.)

What am I missing?
Darran.