Catalyzes the epimerization of trans-4-hydroxy-L-proline (t4LHyp) to cis-4-hydroxy-D-proline (c4DHyp). Is likely involved in a degradation pathway that converts t4LHyp to alpha-ketoglutarate. Displays no proline racemase activity. trans-4-hydroxy-L-proline = cis-4-hydroxy-D-proline Belongs to the proline racemase family.