[en] We present here some striking discrepancies in the results of ac and dc magnetization measurements performed in a single crystal of a low-T_c superconductor, Yb₃Rh₄Sn₁₃. The fingerprint of a transition from an ordered vortex lattice a la Bragg glass (BG) phase to a partially disordered vortex glass (VG)-like phase is unearthed under the influence of an ac driving force present inevitably in the isothermal ac susceptibility (${\mathrm{\chi <!--\; ??\; -->}}^{\mathrm{\prime <!--\; ???\; -->}}(H)$) measurements. In contrast to its well-known effect of improving the state of spatial order in the vortex matter, the ac drive is surprisingly found to promote disorder by helping the BG-to-VG transition to occur at a lower field value in this compound. On the other hand, the isothermal dc magnetization (M–H) scans, devoid of such a driving force, do not reveal this transition; they instead yield the signature of another order–disorder transition at elevated fields, i.e., peak effect (PE), located substantially above the BG-to-VG transition observed in ${\mathrm{\chi <!--\; ??\; -->}}^{\mathrm{\prime <!--\; ???\; -->}}(H)$ runs. Further, the evolution of the PE feature with increasing field as observed in isofield ac susceptibility (${\mathrm{\chi <!--\; ??\; -->}}^{\mathrm{\prime <!--\; ???\; -->}}(T)$) plots indicates the emergence of an ordered vortex configuration (BG) from a disordered phase above a certain field, H* (∼4 kOe). Below H^*, the vortex matter created via field cooling (FC) is found to be better spatially ordered than that prepared in zero field-cooled (ZFC) mode. This is contrary to the usual behavior anticipated near the high–field order-disorder transition (PE), wherein an FC state is supposed to be a supercooled disordered phase and the ZFC state is comparatively better ordered. (paper)