I am not going to suggest there collusion but I can say that my broker told me not to put stop losses on ZEN because the market action on the two previous drops and rebounds in the same day were caused by stop losses being set.
Thats what I was told. Houses buy the the bid down and trigger the stop losses that people have set. This goes on all the time. I for one have been bought out twice b4 on other issues only to find out the stock is now selling at thre original.