Yes, this is a known issue, I have the exact same issue , but I would also try a new USB cable as the mac power output is 500ma, the unit needs over 500ma to work correctly (i know the sticker on the bottom says 500ma but my tests show the unit draws more than 500ma)
So if the mac provides 500ma and you loose 100ma in crappy USB cable then the unit will boot but randomly disconnect, if you load terminal up and view the usb log you will see power related eerors then USB disconnects.
sadly the SB2 will not work via a HUB, so a powered hub is out of the question.
I have tested the SB2 via hub in linux, windows, MAC OSX with 5 different powered and non powered hubs on 3 different computers. Also i have two SB2 and one SB all have same behavior.
darkspr1te