What I can see the last weeks is pretty strange and I am absolutely clueless.
In a nutshell it is like -150 drop a few days, sometimes hours a +130 rise, later again -140 drop.
The funny thing is this happes also for keywords I never built links to. I track also related terms, where I think they could bring buying traffic, but am unsure that it would be effective to push them. One of this keywords has been on #19 and I really never built a single link on it. It dropped down to #240 and then increased about 30 position to about #200, where it stays now.
This is the most strange update I've ever seen here. Strange. And now, I don't believe that this relies only on brand anchored backlinks.