nios2-flash-programmer-gui incorrect EPCS Flash Controller base address in MMU design

I noticed that, in case of an MMU-enabled Nios II design, the nios2-flash-programmer GUI moves the base address of the EPCS flash controller into the untranslated memory area (e.g. 0x00001800 ==> 0xc0001800) and adds the --mmu option for the nios2-flash-programmer tool, but the tool expects the true physical base address instead and uses --mmu to do the translation by itself. That causes the error:

"The EPCS base address must be physical memory address below 0x20000000."

I managed to workaround this by manually changing the translated address back to the physical address in the generated flash_programmer.sh script that is in the staging directory (./script).

What could I be doing wrong to get this error in the first place ?

Interestingly, the --mmu option is not in the Nios 2 Flash Programmer User Guide (Feb. 2010 ed.), but it is nevertheless available (nios2-flash-programmer --help).