Unibios does not open

[Argonautic]

Here is a weird issue I have:
Unibios is supposed to open by pressing C+A+B which corresponds to Y+B+A on non-Neogeo controllers. Wiki However, when I tried that, it didn't work. Through some testing, I found out that the buttons are actually mapped to left (C), up (A) and down (B) on the d-pad (which I obviously can't press at the same time).

Strangely, the NG games work just fine, only the BIOS button combos are somehow swapped.
I already tried several controllers and doublechecked my button config in Emulationstation and Retroarch.

Not sure what the issue is here. Any ideas?