Question Plugging PS/2 Keyboard into Mouse port...and it worked. How is that possible?

[cYpxHSx]

Hello everyone, recently I just had this weird thing that happened to me right now;

Days ago, my friend gave me an old PC as he isn't using it anymore. I checked the motherboard and found out that it's a Socket 478 motherboard PCPartner RS300MS4-A26.
Today, I wanted to try it to see if it still working or not. I hooked everything and tried running it.
The POST section appeared but stopped with this message;

"Keyboard not detected"

as I'm sure I plugged in the right port and turns out, there wasn't any single led on and then pressing F1 or DEL didn't do anything.
I spend half minute, trying everything to fix it but no luck. Then I came up with crazy idea;

"Why not use Mouse port on Keyboard?"

Plugged the Keyboard cable into Mouse port and I shocked the fact that keyboard was working on POST and even on Windows.
Of course with that plugging the keyboard into mouse port, I wasn't able to use mouse... I did felt like this motherboard has Mouse/Keyboard combo that most of new generation motherboards have.

So here is the thing, why is this happened to me?

 

[ElectrO_90]

The mouse/keyboard port are the same connector - it doesn't matter which one it goes into.
Buy a USB mouse and plug that into the USB on the motherboard.
You now have a working PC

 

[cYpxHSx]

The mouse/keyboard port are the same connector - it doesn't matter which one it goes into.
Buy a USB mouse and plug that into the USB on the motherboard.
You now have a working PC

Well, USB Keyboard and Mouse will easy fix alright, but I want to use PS/2 ports as I'm thinking to make it Windows 98 project (I have the PS/2 Mouse and Keyboard). Worst case scenario, will be PS/2 to USB Converter.

But I'm confused on your first sentence, they are looking same but there is reason that they are colored. Normally, on old gen boards it does matter which port you plugged in.
But in this scenario, it's different and weird

 

[ElectrO_90]

You can't, its broken.