I have tried with more than a dozen of copies of the same file with the same lower cased name, with the same MD5.
Recalbox continues to mark it with an "X" for not valid. All the other PSX BIOS are properly recognized.

Is this a bug? Do I just have bad luck?
Filename: "scph101.bin"
MD5: 6E3735FF4C7DC899EE98981385F6F3D0

From what I can tell, all the other MD5s are lower case, but this one is upper case for some reason? Could that be the reason?