This is a limitation in the date handling in php, it should be fixed in php 5, so it should in theory work on eZ Publish 4.0 (but I havn't personally tested this yet).
Alternative is to use the birthday-datatype: http://ez.no/developer/contribs/datatypes/birthday_datatype
Most uptodate version is here: http://svn.ez.no/svn/extensions/birthday_datatype/
Do you know if the manual change i have made on the kernel will be affecting negatively to the performance of ez? the thing is that the templates are already done with the "date" attribute and i would have to change quite a many if i wanna change the attribute type.
