Magic-angle spinning NMR spectra of samples containing dilute spin-1 2 pairs display broadenings or splittings when a rotational resonance condition is satisfied, meaning that a small integer multiple of the spinning frequency matches the difference in the two isotropic shift frequencies. We show experimental rotational resonance NMR spectra of a 13 C 2 -labeled retinal which are in qualitative disagreement with existing theory. We propose an explanation of these anomalous rotational spectra involving residual heteronuclear couplings between the 13 C nuclei and the neighboring 1 H nuclei. These couplings strongly influence the rotational resonance 13 C spectrum, despite the presence of a strong radiofrequency decoupling field at the 1 H Larmor frequency. We model the residual heteronuclear couplings by differential transverse relaxation of the 13 C single-quantum coherences. We present a superoperator theory of the phenomenon and describe a numerical algorithm for rapid Liouville space simulations in periodic systems. Good agreement with experimental results is obtained by using a biexponential transverse relaxation model for each spin site.