  The close correlation observed between emission state and spin-down rate
change of pulsars has many implications both for the magnetospheric physics and
the neutron star interior. The middle-aged pulsar PSR J0738$-$4042, which had
been observed to display variations in the pulse profile associated with its
spin-down rate change due to external effects, is a remarkable example. In this
study, based on the 12.5-yr combined public timing data from UTMOST and Parkes,
we have detected a new emission-rotation correlation in PSR J0738$-$4042
concurrent with a glitch. A glitch that occurred at MJD 57359(5) (December 3,
2015) with $\Delta\nu/\nu \sim 0.36(4)\times 10^{-9}$ is the first glitch event
observed in this pulsar and is probably the underlying cause of the
emission-rotation correlation. Unlike the usual post-glitch behaviours, the
braking torque on the pulsar has continued to increase over 1380 d,
corresponding to a significant decrease in $\ddot{\nu}$. As for changes in the
pulse profile after the glitch, the relative amplitude of the leading component
weakens drastically, while the middle component becomes stronger. A combined
model of crustquake induced platelet movement and vortex creep response is
invoked to account for this rare correlation. In this scenario, magnetospheric
state-change is naturally linked to the pulsar-intrinsic processes that give
rise to a glitch.
