I have a 8x1 WS2812 board (they might be WS2812B, I can't tell). $1 or so on eBay.
I had a problem with "smearing" of the individual led settings (an adjacent WS2812 would flicker with that color even though it should have been completely dark).
I fixed it by increasing the "reset" time (the time used to tell the chips to display their settings) from 50us to 60us. The specs I have state a reset time greater or equal to 50us. 55us reduced the smearing but didn't eliminate it.
So, has anyone else experienced this? I have other WS2811/WS2812 strips that don't have this issue... Maybe just some bad or out-of-spec parts?