There's a known issue with xsd:date elements, they're generated as datetime and thus cannot be imported (at least with data validation) by mendix. We hope to fix this soon.
Note that datetime elements always work correctly.
If you want to be kept updated on when this will be fixed, file a bugreport in our support portal.
The date storage has changed somewhere between 2.4.x and 18.104.22.168. To solve this you can use custom MF mappers. You can use the following javacode if you want to send a date from 2.5 to 2.4.5 (datetime is the argument, a DateTime, and the function returns a string):
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"); format.setTimeZone(TimeZone.getTimeZone("UTC")); return format.format(datetime);
On the 2.4.x side you can convert the String back to a datetime using a java action with:
Date val = ISODateTimeFormat.dateTimeParser().withZone(DateTimeZone.getDefault()).parseDateTime(date).toDate(); return val;
(So instead of using datetimes, strings are used. So you need to add an additional (virtual) attribute for this in your domain model, to store the converted date).