I think that yours issues was fixed in new UVM 1800.2-2017
Note that UVM do not support 8 bits wide memories mapped into map with 32 bits word when byte addressing is off
you will got on 1800.2:
KERNEL: UVM_WARNING uvm_reg_map.svh(1558) @ 0: reporter [UVM/REG/ADDR] this version of UVM does not properly support memories with a smaller word width than the enclosing map. map tst_reg_blk.test_reg_map has n_bytes=4 aub=4 while the mem has get_n_bytes 1. multiple memory words fall into one bus address. if that happens memory addressing will be unpacked.