asterisk users - Mar 2006 - Phase locked mode

Anyone have a hint on what this means:
Mar 13 15:14:58 DEBUG[16772] channel.c: Generator got voice, switching 
to phase locked mode

Just had a user call me and tell me that several times through a 
conversation, the line would just cut out for a little bit and then come 
back, the person on the other end had no clue it was happening.  This is 
what showed in the logs a couple times throughout the conversation, so 
I'm thinking it's the culprit, just don't know what it is exactly.

Aaron