The negative power is a known bug with the mac drivers that your using. You can try reverting to the ieee ones. Ive even posted a guide which you can find in the how-to bt4 section.
The power settings are just reversed so think of -01 as being perfect and -70 or -80 being very weak.
I will also note that i have had some problems using the mac drivers and trying to get handshakes from my AP. I have not however had any problems with the ieee driver.
All that being said it could be how your trying to get the handshake thats the problem, however since you seemed to grab yours perfectly fine i fail to see the point in worrying about it.