Repro steps:
1. Open Scene1 from the attached project.
2. In the scene view, select the particle system, and make sure Bounds are visible.
3. Drag the particle start size and observe how the particles don't find within the bounds.

Expected outcome: the AABB to resize and include all particles.

Notes:
- To a lesser degree, seems like rotation over lifetime can also occasionally throw particles outside the AABB.
- Not a regression, happens in 2017.1