[Zope] ZClass : strange behaviour of a lines item in a propertysheet

Hi Zopistas, I'm making a ZClass with a "lines" property in a propertysheet. I add items in that list with a python script in the methods of that ZClass: mylist = container.list_links ... mylist.extend(items) The stange thing is that sometimes, the items are appended to the list_links property of the object (that's OK), and other times - in an untimely manner - the items are appended TO THE PROPERTY DEFINITION IN THE ZCLASS ITSELF !!!!! Is it a Zope bug ? Has an object has the ability to modify its own class !!!! In that case, it's a big security issue! This has been noticed on a Win32/Zope 2.5.1 box. I did'nt yet try on my freeBSD box. Any idea ? --Gilles