  We study the broadening of initially localized wave packets in a quasi
one-dimensional diamond ladder with interacting, spinless fermions. The lattice
possesses a flat band causing localization. We place special focus on the
transition away from the flat band many-body localized case by adding very weak
dispersion. By doing so, we allow propagation of the wave packet on
significantly different timescales which causes anomalous diffusion. Due to the
temporal separation of dynamic processes, an interaction-induced, prethermal
equilibrium becomes apparent. A physical picture of light and heavy modes for
this prethermal behavior can be obtained within Born-Oppenheimer approximation
via basis transformation of the original Hamiltonian. This reveals a detachment
between light, symmetric and heavy, anti-symmetric particle species. We show
that the prethermal state is characterized by heavy particles binding together
mediated by the light particles.
