[Zope] DateTime Feb 29 error just in Netscape 4?

This is a bit odd. I have some image objects that display fine in IE 4, but in Netscape 4 I get a Zope error Invalid Date-Time String Tuesday, 29-Feb-00 17:53:59 The traceback ends with DateTime.py, line 848, in _parse. Is this a Y2K-leap error, or is something else going on here? I've checked two of these images and in both cases the date it is complaining about is on the 29th. And why only Netscape 4 and not IE? --RDM