pwr_fan connection..

I posted this in "cooling" with no replies.. I decided to try it here..

I added a chassis fan and connected it to the pwr_fan connector on my mobo (sig).. The fan spins at full the whole time, but bios reports the RPM as fluctuating between 0-8000rpm, when i know for a fact the fan is spinning at a steady 2500 or so (80mm fan).. I have another fan connected to cha_fan connection and bios reports it fine.. Also, in motherboard monitor software, the power fan setting tells me the fan is not spinning at all..

Is this because this connection is not intented for a chassis fan (what exactly is it for)?? should I be worried? it seems to work fine except for reporting the rpm.. Is this an issue with the current bios I am running? thanx in advance.

Some PSUs have an extra cable for the fan, which you have to connect to the mobo. I'm using mine to a regular case fan, and it works ok.
But when I had the boxed AMD heatsink and very noisy fan, the ASUS Probe would sometimes say the speed dropped from 5500 RPM or so down to 2000. Since it said 15000 RPM sometimes I stopped using it....
I don't think the RPM values are correct every time, neither in the hardware nor in the software, so if the fan spins on like it should you can just ignore the RPM. If it doesn't cause trouble that is....