Soraka's E is Not Functioning Properly

I've been playing Soraka support a hell of a lot lately. Like ALOT alot. Through playing her numerous times, I've gotten intimately familiar with how her abilities work or are supposed to work. I have however noticed a problem with her E, Equinox.

Sometimes when I cast Equinox on enemies, it does not immediately silence them or prevent them from using abilities. I've seen Fizz's use playful trickster while being inside the zone. I've seen channel abilities continue AFTER the zone is placed upon them. What gives? Is there some sort of lag compensation going on here?