How to reproduce:
1. Open the attached "TimelineBugPaste" project and "Repro" scene
2. Make sure that Timeline window is open and select Timeline A in the Project window --> Assets folder
3. See that the Timeline has a Track named "Unity", copy & paste it in the same Timeline a few times, notice that the naming pattern of pasted tracks is - "Unity (1)", "Unity (2)" and etc.
4. Delete all the pasted tracks and leave only "Unity" track
5. Paste the "Unity" track from Timeline A to Timeline B (its also in the Assets folder) more than once

Expected result: Pasted Tracks follow the same naming pattern - "Unity(1)", "Unity(2)" and etc.
Actual result: All the pasted Tracks are named as "Unity(1)" and don't follow the same naming pattern

Note: Copying and pasting Track from one Timeline to another was present in 2017.1.0b10

Reproducible with - 2017.2.0b1, 2017.1.0b10