DateHandler jsconfig issue with latest?

we upgraded to the latest SS release and noticed that we are getting different results now with the &jsconfig=DateHandler:iso8601 argument to our AutoQuery API. Specifically, when we pass in DateHandler:ut or utm, it returns the appropriate format, but for all other params from the documentation (e.g. ISO8601) the values returned are identical (e.g. 2017-08-20T06:48:13.8970000-04:00, even if we send in iso8601do), as if it isn’t recognizing the argument value being submitted.

TimestampOffset to
DCJSCompatible dcjsc
ISO8601 iso8601
ISO8601DateOnly iso8601do
ISO8601DateTime iso8601dt
RFC1123 rfc1123
UnixTime ut
UnixTimeMs utm

ServiceStack v4.5.15

The DateHandler is working as expected in latest version of ServiceStack, are you overriding the Date serialization? or have any other custom JSON configuration that could be interfering with it?