Using the latest eeloader (eeloader_104e_PAL50.bin) and BIOS (hbios_105_PAL50.bin):
When I program the Harmony with a 128 B ROM everything works as expected.
If I instead use the menu loader (BIOS) I get various weird results (the console typically displays a black screen with gray bands).
If I enlarge the ROM to 4k by simply concatenating 32 copies of it then it works fine.
My guess is the BIOS simply doesn't mirror the ROM across the adress space properly.
For the curious, the ROM in question is an experiment in generative "music", via this thread on pouet