[Zope] date off by one day per year cummulative

Hi all, Zope 2.2.0, displaying a date property from a zclass has been out by one day for a while, trick was just to +1 to the dtml. THought this was fine til dates into 2001 needed to go on and hey, they become one day too far now ... so now I need to add code to determine the year before adding or not. Not good. Quite grim, actually. It only happens when you use the fmt="xyz" to reformat the dates into UK dd/mm/yy (from the default yy/mm/dd). Should I just work around for now, or is this likely to remain like this for a while. If so then zope gets mildly unusable outside the USA. cheers Jonathan