All right all you windwalkers out there, we need to test and post our results to the official forums so that our beloved devs can fix this. Let me explain the problem to those that don't already know it.
Currently on the live servers, can't comment about ptr, when you reach certain haste thresholds you lose 1 tick from your channel. Theoretically you always lose 1 tick under Heroism/Blodlust. The haste thresholds are 6072 for the first thick and 9808 for the second or in channel time 3.5 sec and 2.5. Try to replicate and report your data to the official forums so they can hopefully fix it.