How to reproduce

• use IE 7 or 8
• edit a form
• add a list with 6 values : value1 .. value6
• save
• edit the form

Actual behavior :
values are : value1, value1, value3, value3, value5, value5

Expected behavior :
values are : value1, value2, value3, value4, value5, value6

OK in FF3.5