Repro steps:
1. Open Scene1 from the attached project.
2. Observe the two particle systems in the scene; one has no bursts, the other has 1 burst.
3. Select both systems and observe how in the inspector it appears that none of them have any bursts
4. Add a new bursts
5. Observe how both systems have the same bursts (i.e. even though only 1 burst was added, the first system inherited the pre-existing burst).

Expected outcome: only the new burst to be added.

Notes:
- seems a bit far-fetched to want to multi-add a burst on systems with different pre-existing bursts. Maybe just disable the functionality if the selected systems have different bursts?
- not a regression, reproes in 2017.1 up to 2018.1