Update: I just now went into Ubuntu settings-->displays and switched the Primary Display to monitor #2 (my external monitor), and with that change applied, DT now adjusts itself to fit my display.
DT still fits properly on the laptop screen using these settings, so, for now, although this makes no sense to me, I will use these settings whenever I want to work in DT.
My previous statement that this behavior is related to this current version of DT is probably erroneous.
Still seeking advice. Thanks.