Appt. Date & Time... field will not stay blank (as of today)

Appt. Date & Time... field will not stay blank (as of today)

I have a field that is titled, " Appt. Date & Time" and the corresponding fields (before today) would let me change the date and time, or leave it blank.   But as of today I cannot change it and leave it blank!

I imagine it has something to do with an update.  Does someone else have the same problem?  Fix?