  The present work is a comment on PRL 98, 190401 (2007), arXiv:0705.0667 . The
authors reported NMR measurements in solids with different pulse sequences. In
some multiple $\pi$ pulse echo trains they observed coherent signals of several
seconds, well beyond the Hahn echo decay, $T_{2HE}$ (few milliseconds). They
ascribed the long tails to coherent phenomena arising on the dipolar couplings
during any real finite NMR pulse. Their statement is based on some assumptions
that are incorrect and parameters in the calculations, that do not represent
the experimental conditions.
