Time Dilation currently does not check whether a spell is active in the HUD of the unit or if it is hidden away. This makes it slow some heroes for twice as much for 1 spell.

1. Pick Keeper of the Light and level up Illuminate
2. Create ane nemy Faceless Void and level up Time Dilation
3. Cast Illuminate
4. Get hit by Time Dilation

Result: You get 2 stacks of Time Dilation slow, one for the Illuminate you just have cast, and a second stack for the hidden non-channeled Illuminate, because that hidden spell (which is only active during Spirit Form) goes on cooldown as well whenever the channeled version is cast. Vice versa, when the non-channeled version is cast, the channeled one goes on cooldown as well. This means Kotl will always get 2 stacks of slow for Illuminate, no matter what.

More examples:
1. Song of The Siren's Cancel sub-spell always goes on a 1 second cooldown when Song of the Siren gets cast. This means Song of the Siren cast while affected by Time Dilation also applies 2 slow stacks.
2. Invoker probably suffers the most. Let's say you just used your typical combo in a fight, tornado into blast into meteor into sunstrike. Then you invoke 2 new spells so that tornado, blast, meteor and strike are no longer in your HUD. If you get hit by Time Dilation now, you will get 4 slow stacks, one for tornado, one for blast, one for meteor and one for sun strike (and maybe 1 more for invoke).

Comparison to Rubick:
1. Rubick, who can have many spells "on cooldown", does not get slowed for spells which are on cooldown for him when they are not currently active in his HUD. He only gets slowed for spells which are actually there. He does get a stack if he steals a spell which is still on cooldown for him.

Expected: Time Dilation should ignore spells which are currently hidden. It should only add a slow stack if they get un-hidden (e.g. by activating Spirit Form so that unchanneled Illuminate is there now).