Custom Track not taking my custom PlayableAsset?

Code (CSharp):

1. [TrackClipType(typeof(BotSpawnAsset))]
2. public class BotSpawnControlTrack : TrackAsset {
3.      [...]
4. }

When I drag my BotSpawnAsset onto the custom track it automatically creates a Playable Track and puts it in that one instead. I can then move it up into my custom track, but shouldn't it just be created right there?! What am I missing?