The stock market is a fickle thing, but as Black Friday nears, the Vendors segment has posted another week of cumulative growth, in our Wireless Watch Stock Tracker. Even the Operators managed an increase this week, although sat slightly behind the Indexes. But while the cumulative adjusted average performance, charted in the first graph, suggests that the Vendors have grown 2.59% this week, a major drop by Casa Systems, down some 27 percentage points, drags the true average performance of the segment down to a loss of 1.08% compared to the previous week. This reiterates the complexity of comparisons, but sticking with the Vendors, most were up this week. Cisco was down 1.36%, while CPE-slinger CommScope was down 18.82%, as…