Can someone take a look at Soraka's Equinox?

Playing Soraka a fair bit, I've had a few instances of an enemy champion still casting an ability while on the silenced zone. I would concede that a lot of times, it's because the enemy champion has cast their ability a split second before I cast the silence, and I accept that

But today, I had a particular instance where the enemy Nami got out of position, she just walked up to my Vayne and I, so I immediately put the silence directly beneath her. She Aqua-prisoned Vayne (which I assumed she'd cast the ability before I silenced), but then she proceeded to ult while sitting in the dead center of Equinox. I know she was in the silence field because she then became rooted! (We went on to lose the match, I don't blame that situation for it though, my team simply under-performed)

I don't have proof of this interaction, as I didn't have the foresight to use any recording programs, but I do think this is worth looking into.

TL;DR - A possible bug in which the enemy is still able to cast abilities while in Equinox's AOE silence.