The rt2800usb module is quite buggy, so you have to blacklist it and use rt2870sta instead.

Information

pat@htpc:~$ lsusb
Bus 001 Device 002: ID 148f:2870 Ralink Technology, Corp.

Syslog

htpc kernel: [ 5.273678] Registered led device: rt2800usb-phy0::radio
htpc kernel: [ 5.273689] Registered led device: rt2800usb-phy0::assoc
htpc kernel: [ 5.273710] Registered led device: rt2800usb-phy0::quality
htpc kernel: [ 5.274304] usbcore: registered new interface driver rt2800usb

Blacklist

echo blacklist rt2800usb | sudo tee -a /etc/modprobe.d/blacklist.conf
echo blacklist rt2x00usb | sudo tee -a /etc/modprobe.d/blacklist.conf

Restart and you’re fine.