I've a got a local sandbox running CiviCRM 4.7.18 on Drupal.
For any datepicker field (e.g., Contacts > New Activity), the selection is displayed with munged URLs separating the date components. For example, were I to select today's date, I'd expect to see this value in the text input:
Instead, I get this
Note: the URL of this site is mpk.localhost. In addition to jamming in the site URL instead of separators, some character replacement is happening which might provide a clue as to what's going on:
- "m" is replaced by "6"
- "o" is replaced by 181