Cool that you managed to install the modified cgminer on a Rapsberry Pi.
I used the procedure i found on your blog.
Did you connect the Hashbuster Nano directly to the usb port or thru a (usb 2.0) powered HUB ?
Tried it with and without a powered USB 2.0 hub, makes no difference.
The same hardware setup works without issues together with 10 USB erupters or one HEX16A miner
I'm still a Linux noob but maybe the issues are related to the hidapi config on the raspi. Just a wild guess.
The hasbuster nano works perfectly as i already tried it with the Hashbuster Oracle virtual box session on a 64-bit Windows 7 system.