[Zope] Selection property problem

This is the form: <select name="alignment_text"> <option>left</option> <option>center</option> <option>right</option> </select> When I submit this form the <dtml-var REQUEST> says this (assuming I select 'center'): alignment_text: center With this I want to change a Selection property called 'alignment_text', but it fails to "None" all the time. <dtml-call "propertysheets.text_props.manage_editProperties({ 'alignment_text':_.str(REQUEST['alignment_text']), })"> All other properties are ok, except this one that selection one. What's the trick? ...with selection properties. PS. My HTML (the form) looks the same as is does when you click the Properties tab of this object.