Vladimir can be stunned by Veigar while using Sanguine Pool

As the title suggests, even though Vladimir becomes untargetable during the use of Sanguine Pool, if Vladimir would make contact with any of the edges from Veigar's Event Horizon he will be stunned.

I doubt this is intended (hence why I'm reporting it as a bug), but this has been occurring for years and I'd like to know the reason behind this. A bug like this can't have gone through 4 to 5 years unnoticed, can it?

Reproduction steps:

1. Start up a game with Vladimir on one team and Veigar on the other.

2. Level up Vladimir's Sanguine Pool (W) and level up Veigar's Event Horizon (E).

3. Have Veigar use his Event Horizon.

4. Have Vladimir use Sanguine Pool and "walk" (pool?) into Veigar's Event Horizon.

5. And voila! You now have a stunned and untargetable Vladimir in his troll pool.

Hope to see this get fixed in the future and let me know if this has happened to you at any point. Thanks for reading and have a nice day! :)