Hi,
please try this:
xs:dateTime("2017-07-07T18:30:00.1") - xs:dayTimeDuration("PT1S") = 2017-07-07T18:30:59.1 ?????
or that:
xs:dateTime("2017-07-07T18:00:59.1") - xs:dayTimeDuration("PT1M") = 2017-07-07T18:00:59.1 ?????
I think, there is a bug :(
Best Regards
Jan