While the BIOS time and date setup bug is still present, you can fix the VMU loading/saving. As DK999 said it works for Demul, it also works for NullDC.
Take a save file from NullDC called vmu_data_port01.bin and copy/overwrite it to vmu_save_A1.bin, vmu_save_B1.bin, vmu_save_C1.bin and vmu_save_D1.bin in /system/dc of Retroarch.