How to reproduce:
1. Open the attached "case_1155521-ParticleUnlitDistortion" project
2. Open scene "SampleScene"
3. Inspect the 3 quads and their materials and notice that they all have Distortion on

Expected results: All 3 quads have the distortion effect
Actual results: The quad using "Particles/Unlit" shader does not have the

Reproducible with:
LWRP 5.13.0 (using 2019.1.4f1, 2019.2.0b4)
LWRP 6.7.1 (using 2019.2.0b4, 2019.3.0a4)

Notes:
1. Adding "#pragma shader_feature _DISTORTION_ON" to the shader fixes the issue
2. Couldn't test in the 2018.4 stream due to LWRP 4.10.0 not having the distortion settings on particle shaders