While running CI tests for a application that is implemented in C and Java,
some configuration scripts set the current timezone. The C implemented parts
catch the change just nicely, but the java related parts still report the
default image timezone.
A simple example:
It appears the Java implementation uses /etc/timezone as source, not
dpkg-reconfigure tzdata updates this file as well, so using timedatectl
only won’t be enough (at least not on Debian based systems which run java based