This has nothing to do with summer time. ntp delivers UTC. That is it.
It has no idea of what summer time, winter time, time zones are nor does
it care. It delivers UTC time. All of the interpretation of the time
into things like timezones, summer time, etc are done locally by your
computer and your operating system. Many use a set of files called
timezone files (tzdata) to look up what the relation between time at
your location and UTC is. When politicians decide to change those
relations, (eg by abolishing summer time) new tzdata files are issued
which need to be installed on your system. You do not tell us what your
operating system is etc. Note tht some operating systems leave it up to
you to insititute changes (like your wrist watch which you have to keep
resetting when timezones/summer times/... change)
So your problem has nothing to do with NTP. It is a problem within
the device itself.