In 4.0, a Select list with a selection with an empty value failed the required field validation. In 4.1.1, if any item is selected it is valid, even if that item has no value.
The old behavior worked with Java validation, the new one does not - a selection with a null/empty value submits null, which fails server-side validation.
The problem is in dojo.validate.check() line 100 in the current snapshot.
Since this is in Dojo, that behavior may be the desired default, but Tapestry needs a modified behavior with an additional condition - if the element is a select-one or select-multiple, if it has a selection that selection (or at least one of the selections) must not have an empty value.