Demographic dates cannot be keyed in

When entering/editing the demographic date fields - both Birth Date and Deceased Date - through the administrator interface, the field refuses to accept a date. When using the date selector, it enters the word "birth", and when keying in the date, the only characters it will accept are the letters b i r t h. "birth" of course is an invalid entry, so the data is not saved, though if a proper date had already been stored before this bug, that date can be deleted.

Users are able to enter proper dates into front-end profiles, and those dates are stored correctly.

I was unable to replicate in the Joomla demo, but I am using 4.7.16 on Joomla 3.6.5, and the demo is 4.6. This seems to be a recent bug, but I cannot pin down which version broke it.