  The relative abundances of singly-deuterated methanol isotopologues,
[CH$_{2}$DOH]/[CH$_{3}$OD], in star-forming regions deviate from the
statistically expected ratio of 3. In Orion KL, the nearest high-mass
star-forming region to Earth, the singly-deuterated methanol ratio is about 1,
and the cause for this observation has been explored through theory for nearly
three decades. We present high-angular resolution observations of Orion KL
using the Atacama Large Millimeter/submillimeter Array to map small-scale
changes in CH$_{3}$OD column density across the nebula, which provide a new
avenue to examine the deuterium chemistry during star and planet formation. By
considering how CH$_{3}$OD column densities vary with temperature, we find
evidence of chemical processes that can significantly alter the observed column
densities. The astronomical data are compared with existing theoretical work
and support D-H exchange between CH$_{3}$OH and heavy water (i.e., HDO and
D$_{2}$O) at methanol's hydroxyl site in the icy mantles of dust grains. The
enhanced CH$_{3}$OD column densities are localized to the Hot Core-SW region, a
pattern that may be linked to the coupled evolution of ice mantel chemistry and
star formation in giant molecular clouds. This work provides new perspectives
on deuterated methanol chemistry in Orion KL and informs considerations that
may guide future theoretical, experimental, and observational work.
