It is not common to just GSF as it happens in BG stunted ponds also. I will find the prior thread where it is discussed. Not so much all the LMB yoy being eaten but also that the LMB sense the situation and won't spawn.

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=20;t=003757