This isn't on a mini but on an i7 Hackintosh I've got. I had very similar problems. I bought a mini BT
adapter from ebay and it was recognised and found my magic mouse which worked fine.
Later though when I added the Apple Keyboard, it would see it and not recognise. I tried unpairing them and it then saw the keyboard but not the mouse!
After a bit of testing, I could establish that it worked with the first device connected, but could see subsequent ones.
In the end I bought a branded one from PC World for Â£10 and it's worked absolutely fine with multiple devices. I just put it down to the first one being cheap and rubbish