Bug in Daffodil with calendar properties?

[Roger L Costello]

This datetime input:

20230926T124800Z

Parses to this:

<DateTime>2023-09-26T12:48:00+00:00</DateTime>

And unparses to this:

20230926T124800+0000

Notice ... +0000 ... why isn't it Z?

Here's the DFDL:

    <xs:element name="DateTime" type="xs:dateTime"
        dfdl:calendarPatternKind="explicit"
        dfdl:calendarCheckPolicy="strict" 
        dfdl:calendarPattern="yyyyMMdd'T'HHmmssZ"
        dfdl:calendarFirstDayOfWeek="Monday"
        dfdl:calendarDaysInFirstWeek="7"
        dfdl:calendarTimeZone="UTC+6"
        dfdl:calendarLanguage="en" />