Dragging Audio assets onto the Sequencer timeline will create a new audio track when dropped onto an object's audio subtrack

Dropping audio assets onto audio subtracks in the timeline adds them to a regular audio track instead. 

1. Create a new level sequence
2. Add a cube to the world then add it to the sequence
3. Add an audio subtrack to the cube through the "+" add track menu (any editor audio asset will work)
4. Browse to an audio asset in the content browser
5. Drag the asset onto the timeline of the audio subtrack you just created
6. Drop it onto the track when it is outlined in green

RESULT
A new audio track is created instead of adding to the existing subtrack. Note that when dropping onto a regular audio track (one that is not a subtrack) the asset will behave as expected.