Big Muff Triangle volume pot problem

[noisemaker]

I just finished my sixth project, the big muff triangle http://www.diystompboxes.com/pedals/triangleMuff.jpg and everything is working fine except the volume pot (100K audio), which is acting funny.

The sweep, when I measure the resistance, is fine, but when I plug the thing in and adjust the volume pot, the volume level starts at about 50% volume and stays steady until about 75% of travel, and then it dips to zero, then back up to normal level within about 10 degrees of travel, then normal after that.

I've switched out the pot with no change. I've checked my soldering and everything seems fine. I'm using 5088's and everything else is true to the schematic. The only thing maybe out of the ordinary is that the voltages on the emitter and base (but not the collector) of the transistor before the volume pot are about one volt higher that the other transistors. I've got e=1.19/b=1.78/c=3.85/batt=9.27.

Side note: Having never played thru a big muff before, I was wondering what all the fuss was about. Now I know. 

Thanks in advance for any help.