[Zope] boolean property bug

Probably I found a bug in handling boolean properties in Zope 2.2.0. I can only set them "on", and then can't turn "off". I can have default value "off" (in ZClass definition), but after first switch to "true", it can't be changed. It only refers to handling properties via Zope's management screens. API functions manage_changeProperty, manage_editProperty work fine, so maybe it's an error in generated HTML forms, or in processing of these forms. ololo