Your provided command does not work in a command block, and only works from chat because whitespace is trimmed out: MC-65034
I just double checked this and you are indeed correct. Turns out the mcedit-filter to import Command Block commands from textfiles that I was using before also trims whitespace.
However, I still consider the current behaviour a bug considering almost every single compiler and interpreter out there doesn't care about extra spaces and tab stops (and neither do any minecraft data files) in order to make writing and reading code not painful. 🙂
Effect levels above level 4 aren't officially supported. (Not supported as in if they cause issues, it is your problem and not something Mojang will fix.)
This is an issue present in all versions that use generic.followRange.
Considering spawning 20 Zombies with a 160 block follow range in version 1.8.9 creates no noticeable lag whatsoever whereas spawning only one in 16w02a makes the game basically unplayable, I find that very hard to believe.
Considering everything else that is exposed to end users in the game is translatable I'm pretty sure this fulfills any definition of a programming oversight which is what bugs are.