For Council, why on earth would you take FoN? For 4 targets, Incarnation is better in simulations and FoN doesn't even work at it's optimal capacity when switching targets. Especially if you have the fight last just over 3.5/6.5/etc. minutes, Incarnation shines even more.
About the haste bugging, they only happen when the treants' cast gets below 0.5 seconds. This is very rarely the case and should be considered only under the effects of Bloodlust/TW/Heroism, the meta gem and Nature's Grace.