Former single-crystal and powder X-ray diffraction studies of 9,10-dimethyltriptycene (1) and its isotopomer-d12 selectively deuterated in the aromatic positions (1a) consistently delivered undistorted R3̅c structure of the material. On the other hand, 1H wide line NMR spectra of polycrystalline 1a reported by us previously were incompatible with the above structure. The presently reported 1H spectra of a single crystal of 1a shed new light onto these discrepancies. These spectra reveal two sharply defined environments of the methyl groups in the investigated crystal, of which only one is consistent with the R3̅c structure. In it, the methyl groups from neighboring molecules come as closely spaced pairs of D3d symmetry, coupled by intermolecular proton–proton dipole interactions. The other environment encompasses as much as about 20% of the methyl groups. They also appear to fit the R3̅c lattice but, at variance with those occurring in pairs, do not show dipole couplings to their neighbors. Despite these differences, both sorts of the methyl groups show the same thermally activated dynamics, what was confirmed by line shape fits to variable temperature spectra of the investigated crystal. The diverse properties with respect to intermolecular dipolar couplings cannot be explained in terms of a static disorder, with the isolated groups facing voids in the lattice. This interpretation is untenable because no sufficient deficit in the crystal’s specific weight was observed. Moreover, no foreign electron density, possibly originated from solvent molecules occluded in the crystal voids, could be detected in the X-ray studies. The fact that some sort of disorder occurs in the investigated crystals is indicated by the presence of diffuse scattering features in the X-ray data. A tentative explanation of these observations in terms of a dynamic disorder of a hitherto unreported type is proposed. It calls for further intense research to elucidate connections between diffuse scattering of X-rays and possible types of disorder in molecular van der Waals crystals of organic compounds.