Note: this issue is in the dpath branches, not the current 0.15.0

In the XPath implementation of Daffodil, if you provided the xs:date constructor with a date like the following: 1991-03-4, you would get this error:
Invalid date "1991-03-4" (Day must be two digits). Now the function accepts sincle-digit days and it parses as 1991-03-04+00:00.

This may be our expected behavior but I thought I should note the discrepancy.
See test test_date_constructor_01 in the following file:

daffodil-test/src/test/resources/edu/illinois/ncsa/daffodil/section23/dfdl_functions/Functions.tdml