Reproduces in SRP 7.1.8 and 4.10.0. Could not test master as it has compile errors.

Repro steps:
1. use a project with both HDRP and Universal/LWRP packages
2. Create an HDRP and URP/LWRP pipeline asset
3. Open a scene with a directional light
4. Switch the pipeline in graphics settings to the HDRP asset
5. Switch the pipeline to the URP/LWRP asset
6. Select your directional light and set the intensity to something else
7. Enter and then exit play mode
8. Check the intensity value in the inspector
Expected result: the intensity stays the same
Actual result: the intensity value changes back to what it was
Cause: The HD Additional Light Data script that gets added to the light when HDRP is set as the current pipeline (disabling this script will stop the bug from reproducing)

Note: This would probably be a high pain point for users creating asset store assets and testing in both HDRP and Universal/LWRP, due to the fact that you need to change the light intensity to drastically different values for each RP since HDRP uses real world light values and Universal/LWRP doesn't.