The spec clearly indicates the ToDateTime(Date) operator will return a DateTime with the time components unspecified. The following tests validate this behavior (from the published spec test suite):

ToDateTimeDate
ToDateTimeTimeUnspecified

These tests were missing from the test suite in the engine, and when I added them, they fail because the ToDateTime implementation in the engine is setting time components to 0. I've added these failing tests to the skip list, but the ToDateTime behavior should be corrected.