Birthday field broken

There are two ways to reproduce this problem, and no obvious workaround that I can see.

Inline editing:

1. Visit a contact's summary screen. In the right column, click on the field group which contains "Gender," "Date of Birth," and "Age."
2. Select a birth date.

Old-school editing:

1. Visit a contact's summary screen and click the "Edit" button.
2. After the page loads, expand the "Demographics" accordion.
3. Select a birth date.

Instead of a date in the input field, the word "birth" is displayed. An error message is displayed to the right of the field: Please enter a date between birth and birth.

I reproduced this on CiviCRM 4.7.16 on both WordPress and Drupal. This problem appears to have been introduced with the 4.7.16 release, as I cannot reproduce it on 4.7.15 instances.