Odd fact about AES stereo out

I currently have two home systems, NEO AES 3-4 and NEO AES 3-6 revision boards, respectively. I hooked them up to a stereo receiver via the headphone socket and find out the right and left channels are reversed in the two systems. For instance, in Nam-75 at the end of level 1 when the bosses appear on screen, the shorter one is on the left and says "your operations have been watched" and the taller one is on the right and says "you will die". You would expect the former line to come from the left speaker and the latter from the right speaker but this only happens on the NEO AES 3-4, the NEO AES 3-6 being the other way round. How can it be that SNK made such a stupid mistake? Anyone else noticed such a discrepancy between different AES revision boards?

edit: It may be noted that the 3-4 board has the same headphone circuit as multi-slot MVS boards while the 3-6 is different.

stereo

I have noticed the same thing on all the neogeo aes systems I have owned the left and right were reversed