  We present a detailed $^7$Li- and $^{31}$P-NMR study on single crystalline
LiMnPO$_4$ in the paramagnetic and antiferromagnetic phase (AFM, $T_N \sim$ 34
K). This allows us to determine the spin directions in the field-induced
spin-flop phase. In addition, the anisotropic dipolar hyperfine coupling tensor
of the $^7$Li- and $^{31}$P-nuclei is also fully determined by orientation and
temperature dependent NMR experiments and compared to the calculated values
from crystal structure data. Deviations of the experimental values from the
theoretical ones are discussed in terms of Mn disorder which is induced by
Li-disorder. In fact, the disorder in the Mn-sublattice is directly revealed by
our diffuse x-ray scattering data. The present results provide experimental
evidence for the Li-diffusion strongly coupling to structural distortions
within the MnPO$_4$ host, which is expected to significantly affect the
Li-mobility as well as the performance of batteries based on this material.
