Zed Ult + Spell Shield Interactions

I was watching a League video the other day, and I learned that the detonation of his ultimate cannot be blocked by spell shields, only the initial application can. This seemed a bit strange to me and reminds me of a change to Zilean Q that was made a while back for the sake of clarity. While I realize that there is a difference in that Zil's bombs are instant application, whereas Zed's ult has an animation, I feel this would be a good readability and counterplay change nonetheless.

I assume this is how Vladimir's ult works as well; you can spell shield the detonation of the virulent plague? If not, my thoughts are the same for that case. I believe it should. If it does, I don't see why Zed's should be any different.