GDB might not be able to disassemble it, but the assembler and disassembler appear to be in sync.
Running the following:
echo "lf.rem.s r4,r5,r6" | or32-elf-as; or32-elf-objdump -d a.out
indicates that it is getting assembled and disassembled OK. Perhaps it's the way GDB is looking at the tables? Do you know the hook GDB uses to access these tables? Or are they included in the GDB source?