Weird keyboard/case fan behaviour

[lambo603]

Hello

 

So I've got the weirdest issue imaginable, something I've never heard of before 

 

I bought a brand new Corsair K95 Platinum XT (MX Speed Silvers) and it works perfectly fine.

However when I went to turn off my PC for the first time, I noticed that my case fans were still spinning WITH THE PC OFF.

 

I then unplugged the keyboard since that's the only piece of hardware I added to it since yesterday, and they turned off, then when I plugged the keyboard back in, with the PC still off, they turned back on.
Now I have narrowed it down, that when I only use 1 connector, the 1 with the keyboard logo on the USB housing, it's not doing it, yet when I plug BOTH the connectors, keyboard and USB passthrough in, it will turn the case fans on even when the PC is completely POWERED OFF (psu switch is still on).

I've plugged a lot of different USB devices in, and none of them do that, even my old keyboard, Roccat Ryos MK FX which also has 2 plugs does not do it.

 

Do you guys think it's the keyboard's issue or is there something I haven't tried yet?

 

My case fans are controlled by the original fan hub inside the Be Buiet Pure Base 500FX, so it's connected to ARGB, sata (for power) and the fan header, doesn't even have a direct link to the USB (controller).

Motherboard is the AsRock B450 Steel Legend.

 

Has anyone heard of such weirdness before? 

 

Hoping for some answers before I return it on Monday.

 

Kind regards

lambo603