Steps to reproduce:

1. Download and import attached project.
2. Open scene main.
3. Press play or simulate particle system in editor

Expected result: Particles scale equally on all axis.
Actual result: Particles are scaled only on X axis.

Notes: This happens only when 3D start size is set, but Size over lifetime separate axis are not set. It seems that it still thinks that it is separate axis because of 3D start size.

Reproduced on 5.4.0b12