  We present the results of a muon-spin relaxation ($\mu^{+}$SR) investigation
of the crystalline organic radical compound
4-(2-benzimidazolyl)-1,2,3,5-dithiadiazolyl (HbimDTDA), in which we demonstrate
the hysteretic magnetic switching of the system that takes place at $T = 274
\pm 11\,\mathrm{K}$ caused by a structural phase transition. Muon-site analysis
using electronic structure calculations suggests a range of candidate muon
stopping sites. The sites are numerous and similar in energy but,
significantly, differ between the two structural phases of the material.
Despite the difference in the sites, the muon remains a faithful probe of the
transition, revealing a dynamically-fluctuating magnetically disordered state
in the low-temperature structural phase. In contrast, in the high temperature
phase the relaxation is caused by static nuclear moments, with rapid electronic
dynamics being motionally narrowed from the muon spectra.
